Atlanta Braves (2016–2022)
On December 9, 2015, the Diamondbacks traded Swanson, Ender Inciarte, and Aaron Blair to the Atlanta Braves for Shelby Miller and Gabe Speier. The Braves were in the middle of a rebuild, and president of baseball operations John Hart said the team "wanted to make it painful for [Arizona] with players that we got back" by refusing a Miller trade until they received significant prospects like Swanson. After spending spring training with the Braves, Swanson was sent to the High–A Carolina Mudcats. He played 22 games there, batting .333 with a Carolina League-leading 12 doubles, before receiving a promotion to the Double-A Mississippi Braves at the end of April. Swanson spent the first part of the season in competition with Ozzie Albies for a future starting shortstop role in Atlanta, but in July, Albies, who had been playing in Triple-A, was sent down to Mississippi so that he and Swanson could practice as a second base-shortstop pair. That season, Swanson was selected to appear in both the Southern League All-Star Game and the All-Star Futures Game. He appeared in 84 games for Mississippi, batting .261 with eight home runs and 45 RBI. In 105 games between Carolina and Mississippi, he batted .275 for the minor league season, with nine home runs and 55 RBI in 411 at bats.
Swanson was called up to Atlanta on August 16, 2016, after the Braves traded shortstop Erick Aybar to the Detroit Tigers to clear the position for him. He made his MLB debut that day, recording his first two major league hits, both singles, in a 10–3 loss to the Minnesota Twins. His first major league home run, coming in the second inning of a 9–7 loss to the Washington Nationals on September 6, was inside-the-park: the hit off of Gio Gonzalez went over Trea Turner and ricocheted off the center field fence, and Swanson beat Bryce Harper's throw home to record the run. It was the first inside-the-park home run for the Braves since Wes Helms in 2001, and Swanson was the first Brave since Paul Runge in 1985 to have his first career home run fall inside the park. He remained with the Braves through the remainder of their 2016 season, finishing the year with a .302 batting average, three home runs, 17 RBI, and 11 extra-base hits. Swanson had at least one hit in 25 of the 38 games in which he played.
Swanson was the only rookie to make the Braves' 2017 Opening Day roster, joining Chase d'Arnaud, Freddie Freeman, Adonis Garcia, Jace Peterson, and Brandon Phillips in the infield. He began the season in a sophomore slump both offensively and defensively: by the end of May, Swanson was batting .185 with a .559 on-base plus slugging (OPS), while he had also committed 11 errors at shortstop. His struggles coincided with the arrival of Johan Camargo and Matt Adams, both of whom provided offensive power to the infield. Camargo, in particular, had taken over the majority of playing time at shortstop, while Ozzie Albies had just received a major league promotion. On July 27, Swanson was demoted to the Triple-A Gwinnett Stripers, where he could receive more regular playing time. At the time, he had been hitting .213 with six home runs and 35 RBI in 95 games. Additionally, he only had three hits in 25 at bats following the All-Star break. In 11 games for Gwinnett, Swanson hit .237 with one home run and five RBI. He was suddenly called back up to the Braves on August 9 after Camargo suffered a knee injury during his pre-game ritual. After returning to Atlanta, Swanson settled back into the shortstop position, batting .337 with a .434 OBP in the month after he replaced Camargo. Defensively, he and Albies, now playing second base, formed a strong middle-infield tandem. Swanson finished his first full season in Atlanta batting .232 with six home runs and 51 RBI in 144 games and 488 at bats.
Swanson began the 2018 season on a hot streak, recording multiple hits in four of the Braves' first six games. He began feeling discomfort in his left wrist at the end of April, and after aggravating the injury during a game against the New York Mets, he was placed on the 10-day disabled list on May 4. The injury seemed to coincide with a sudden drop in offensive power from Swanson: after batting .358 with a .976 OPS in his first 16 games, he dropped to batting .191 with a .468 OPS in the next 12. After a rehabilitation game in Double-A, Swanson returned to the Braves' lineup on May 19. He again struggled through most of the season, batting .234 with a .704 OPS between June 1 and August 21, a stretch that ended with Swanson's first career multi-home run game. After hitting off of Pittsburgh Pirates starting pitcher Ivan Nova in the fifth inning, he hit another home run in the seventh against reliever Michael Feliz, helping the Braves to a 6–1 win. He widened his batting stance in August and showed some improvement, batting .297 with six home runs between August 11 and September 2, but he hit only .161 in September.
On September 25, 2018, Swanson left a game against the New York Mets in the second inning with wrist pain, later revealed to be a partially torn ligament in his left hand that ruled him out for the remainder of the regular season. He continued to feel discomfort afterwards and was prevented from playing in the 2018 National League Division Series (NLDS). Instead, Charlie Culberson filled in at shortstop during the Braves' postseason run. The Braves lost to the Dodgers in the four game NLDS, while Swanson's hand and wrist continued to bother him until November 5, when he underwent surgery to remove a loose piece of cartilage. The cartilage had been moving around his wrist, and Swanson described the experience as "like if you would slam a wedge doorstop into a door". In 136 games, Swanson batted .238 with 14 home runs and 59 RBI, while defensively he improved from −7 Defensive Runs Saved in 2017 to 10 in 2018.
With his wrist no longer bothering him, Swanson showed a new offensive power during 2019 spring training, giving manager Brian Snitker hope that his production would increase. He seemed poised for a breakout through the first half of the season: by June 18, Swanson's 13 home runs were one shy of his previous career high, and his exit velocity, launch angle, and hard-hit rate at the plate all showed significant increases from the previous season. By the All-Star break, Swanson was batting .270 with 17 home runs and 57 RBI. On July 23, however, Swanson landed awkwardly on first base while attempting to run out a ground ball in a game against the Kansas City Royals, injuring his left heel in the process. The injury initially seemed minor, but he suffered a setback at the beginning of August, and after three weeks on the injured list, Swanson referred to the heel as "a frustrating injury". He was activated from the injured list on August 26, just over a month after suffering the injury. He struggled to hit after returning from the injury, batting only .141 in his first 23 games back from the injured list, but finished the season with eight hits in four games. In 545 plate appearances during the 2019 regular season, Swanson batted .251 with 17 home runs and 65 RBI.
After missing the previous year's postseason, Swanson was named to the Braves' roster as they faced the St. Louis Cardinals in the 2019 NLDS. In the ninth inning of Game 3, Swanson hit an RBI double off of Cardinals closer Carlos Martínez to tie the game 1–1. Adam Duvall followed this with a two-RBI single, and Mark Melancon held the Cardinals scoreless in the bottom of the ninth to win the game 3–1 for Atlanta. The Cardinals held on to win the series, however, with a 13–1 rout of the Braves in Game 5 to eliminate Atlanta from the playoffs. He went 5-for-18 at the plate during his first postseason run, with two RBI and three runs scored.
On January 10, 2020, Swanson agreed to a one-year, $3.15 million contract extension with the Braves. He had an immediately strong start to the 2020 season, which began in July and was shortened to only 60 games due to the COVID-19 pandemic. The Braves began their abbreviated season with a three-game series against the New York Mets, during which Swanson went 5-for-12 at the plate with a double, a home run, and six RBI. He hit his first walk-off home run on August 17, lifting the Braves to a 7–6 victory over the Washington Nationals. On September 9, Swanson was one of three Braves who scored five runs in the Braves' 29–9 rout of the Miami Marlins, a franchise record for the most runs in one game. Austin Riley and Adam Duvall also scored five runs apiece. Swanson played in all 60 games of the pandemic-shortened 2020 season, setting career highs with a .274 batting average, .345 on-base percentage, and .464 slugging percentage while recording 10 home runs and 35 RBI. His 49 runs scored were the third in MLB, behind teammate Freddie Freeman's 51 and Fernando Tatis Jr.'s 50. After the season, which was played without spectators in attendance due to COVID-19 safety protocols, Swanson said that playing in empty ballparks "felt like backyard baseball a little bit", and the lack of audience distractions led players "to feel comfortable in their own skin".
The Braves faced division rivals the Miami Marlins in the 2020 NLDS. Swanson's five RBI in the three-game series were the most of any Braves shortstop during a Division Series, while Atlanta advanced to the National League Championship Series (NLCS) for the first time since 2001. The Braves lost the 2020 NLCS to the Los Angeles Dodgers in seven games, and Swanson cost the team a potential scoring opportunity on a fourth-inning baserunning error. He broke for home plate on a ground ball from Nick Markakis and was caught in a rundown by third baseman Justin Turner and catcher Will Smith. Smith tagged Swanson out and then threw the ball back to third base, where Dodgers shortstop Corey Seager tagged out Austin Riley, who had tried to advance from second base during Swanson's rundown. The Braves had been leading 3–2 at the time of the double play, but ultimately lost the game 4–3.
Swanson filed for salary arbitration during the 2020–21 offseason, but arbitrators denied his request to make $6.7 million the following year, instead ruling that his salary would be $6 million. He began the 2021 season in a slump, batting only .209 with a .631 OPS and 31.4 percent strikeout rate by May 20, but began to pick up in May, with four home runs in a 13-game stretch. On June 3, both Swanson and his middle infield partner Ozzie Albies recorded the 500th hits of their MLB career. Swanson's came on a home run that traveled 440 feet (130 m), the longest recorded during his time with the Braves. On July 22, Swanson hit his first major league grand slam, hitting against Matt Moore of the Philadelphia Phillies in a 7–2 Atlanta victory. It was his 17th home run of the season, tying Swanson's career high. He recorded another grand slam the following week, against John Curtiss of the Milwaukee Brewers. Swanson had hit a two-run home run earlier in the game, giving him 20 for the season, tying Denis Menke for the most of any Braves shortstop in one season. His next home run, which came against the Washington Nationals on August 13, gave Swanson the single-season home run record for any Braves shortstop. He played in 160 games during the 2021 regular season, the most of anyone in the National League, and batted .248 with 27 home runs and 88 RBI in 588 at bats.
The Braves clinched the NL East for the fourth consecutive season on September 30, 2021, with a 5–3 win over the Phillies. Swanson was instrumental in that process, with two doubles, a home run, and five RBI in the last six games before the Braves clinched the title. Swanson's defensive abilities were on display against the Brewers in the 2021 NLDS: in Game 3, he held Milwaukee scoreless on separate occasions, first by preventing runners from advancing on a groundout from Lorenzo Cain and then by turning an eighth-inning double play to retire Jace Peterson and Willy Adames. He was less adept at the plate, going only 3-for-15 in the four-game series. The Braves faced the Dodgers in the 2021 NLCS, where in Game 1 Swanson tagged out Chris Taylor to prevent Los Angeles from breaking a 2–2 tie in the top of the ninth inning. The Braves won the game 3–2 on a walk-off RBI single from Austin Riley. His offensive troubles continued, however, with only two hits in 23 at bats during the six-game series. By Game 4 of the 2021 World Series, Swanson was only batting .225 in the postseason, and he had mostly gone hitless. In the seventh inning, however, he hit a 95 mph (153 km/h) fastball from Houston Astros reliever Cristian Javier for a game-tying home run. Jorge Soler's home run secured a 3–2 victory for Atlanta, putting them one game within reach of their first championship since 1995. With the Astros down 7–0 in Game 6, Swanson secured the final out of the game to give the Braves the World Series championship title.
Swanson's salary for the 2022 season was decided via the arbitration process. He asked for and received $10 million. Swanson was named to the 2022 Major League Baseball All-Star Game roster. On September 30, 2022, Swanson hit his 100th career home run, off New York Mets pitcher Jacob deGrom. Swanson was the only player in Major League Baseball to start all 162 games of the season. He struggled in the playoffs, batting .176 in the four-game loss to the Phillies in the NLDS. Swanson won his first Gold Glove Award at the end of the season. He became a free agent at the conclusion of the season.
