Acting career
In 2018, Fedelin participated as the Hope Pool Son of Cavite in the first batch of Pinoy Big Brother: Otso as a housemate. He is the first male housemate to enter and the last male housemate to leave the house after he was evicted in the last eviction (Day 57 - January 2019) of the first batch earning the 5th place. The Big 4 slot went to Kaori Oinuma, Karina Bautista, Jelay Pilones, and Lie Reposposa.
In 2019, months after being evicted in Pinoy Big Brother, Fedelin starred in the psychological horror film, Abandoned, with Beauty Gonzalez. He then became a part of Kadenang Ginto and landed a role as Mikoy Sarmiento, who is the love interest of Marga Mondragon played by Andrea Brillantes. Thus, SethDrea loveteam was formed. Because of the success of Kadenang Ginto, the Gold Squad was formed. Fedelin together with his co-stars in Kadenang Ginto, Andrea Brillantes, Kyle Echarri, and Francine Diaz became the members of the squad.
In 2020, after Kadenang Ginto ended, the Gold Squad starred in Huwag Kang Mangamba with award-winning actresses, Eula Valdez and Sylvia Sanchez. They also starred in season 1 of Click, Like, Share, where Fedelin acted alongside Jimuel Pacquiao, the son of the former professional boxer, Manny Pacquiao, in the episode Trending.
In 2021, Fedelin, together with Andrea Brillantes, starred in an iQiyi series, Saying Goodbye with Kobie Brown, Andi Abaya and Nio Tria, the son of actress Cherry Pie Picache.
In 2022, he starred in Lyric and Beat with Andrea Brillantes, Darren Espanto, AC Bonifacio, Kyle Echarri, Angela Ken, Jeremy Glinoga and Sheena Belarmino. It was disclosed by Andrea Brillantes that she and Fedelin had maintained a private relationship spanning over two years. This is the last series of Fedelin and Brillantes after both of their loveteam and real life relationship ended.
In 2023, the pairing of Francine Diaz and Seth Fedelin were tested for the first time with their new drama series Dirty Linen by ABS-CBN and Dreamscape Entertainment in 2023. The loveteam called FranSeth were formed and both of them starred in the series called Fractured with Kaori Oinuma, Jeremiah Lisbo, Daniela Stranner, Raven Rigor, and Sean Tristan. The story is about a group of influencers who finds themselves trapped in a disappointing island resort.
In 2024, FranSeth debuted in the 50th Metro Manila Film Festival with their first-ever movie together, My Future You. The film received 10 nominations and won four awards, including Best Director, Best Editing, and 3rd Best picture, wherein Fedelin won the Breakthrough Performance in the Gabi Ng Parangal.
In 2025, Fedelin won the Best Actor award at 2025 Manila International Film Festival held at Los Angeles, California for the movie My Future You. He also starred in a series called Sins of the Father with Gerald Anderson, Shaina Magdayao, Jessy Mendiola, JC de Vera, RK Bagatsing, and Francine Diaz. He then starred in Shake, Rattle & Roll Evil Origins, an official entry to the 51st 2025 Metro Manila Film Festival, with Francine Diaz, Fyang Smith, JM Ibarra, Manilyn Reynes and many more.
In 2026, Fedelin starred in the movie She Who Must Not Be Named with Francine Diaz, Bobby Andrews, Ruby Ruiz, Kat Galang, Elijah Alejo, Raven Rigor, Abdul Raman, Kaleb Ong, and Kych Minemoto.
