Recurring
Dennis Boutsikaris as Malcolm Croft, a professor at MIT and Liam's mentor
Erica Luttrell as Claire Rayburn, Senior Adviser and later White House Chief of Staff to President Monroe Bennett.
Tovah Feldshuh as Pauline Mackenzie, the President of the United States
Josette Jorge as Karissa (season 1), Darius' assistant
Sasha Roiz as Monroe Bennett, the vice president, and later president, of the United States
Mark Moses as Hugh Keating, Grace's father and former CIA agent
Brian Markinson as Randall Calhoun (season 1), the United States Secretary of Defense who is later fired by President Mackenzie and replaced by Harris Edwards.
Jeffrey Nordling as Daniel Hayes (season 1), Jillian's father and a bookseller
John Noble as Nicholas Tanz, Darius' uncle and Chairman of the Board of Directors at Tanz Industries.
Raven Dauda (season 1) as Harris' secretary
Autumn Reeser as Theresa (season 1), aka Tess, Darius' first love
André Dae Kim as Dylan Edwards (recurring season 1, guest season 2), Harris' son and a member of the hacker organization RE/SYST
Taylor Cole as Fiona Lane (guest season 1; recurring season 2), a bartender with whom Harris Edwards has an affair, but who later is revealed to have a connection to Darius' plans to save humanity
Madison Smith as Nate Ryland (season 2), a co-worker, a later friend, of Jillian's in the White House
Jonathan Silverman as Roland Kavanaugh (season 2), the White House Counsel
Anjali Jay as Dr. Rosetta Stendahl (season 2), an old friend of Darius' and a brilliant scientist. She joins Darius and leads the project to prepare a rail-gun intended to help divert the asteroid.
Luke Arnold as Bass Shepherd (season 2), the spiritual leader of Children of Planet Earth (COPE), a support group that Jillian joins
Manoj Sood as Dr. Chandra (season 2), an international specialist in Orbital Dynamics and General Purturbation Theory
James Lesure as Trey Thompson (season 2), a two-term congressman and former NASA pilot who is later named Vice President under Tanz.