Main •
Noah Wyle as
Tom Mason, a former Boston University military history professor who becomes the second-in-command of the 2nd Massachusetts resistance, about 300 civilians and fighters fleeing Boston, fallen to invading aliens. He has three sons: Hal, the oldest, Ben, the middle child who was taken by the Skitters, and Matt, the youngest. His wife died a short time after the invasion while gathering supplies. He becomes friends with Anne Glass, and more. •
Moon Bloodgood as
Anne Glass, the 2nd Mass's doctor. She was a pediatrician before the invasion. She supports civilians' rights to Weaver. Her husband and son were killed during the invasion, and she regrets having no photographs to remember them. •
Drew Roy as Hal Mason, Tom's oldest son. He is 16 years old, and a Scout in the 2nd Mass. His first girlfriend is Karen, although other girls do flirt, and he becomes closer to Maggie after Karen is taken. •
Jessy Schram as Karen Nadler, a teenage girl who works as a Scout in the resistance army. She lost her family in the invasion. Hal is her boyfriend. She is captured by the aliens, harnessed, and works for them. •
Maxim Knight as Matt, Tom's youngest son. His birthday wish is that everything return to before, but he soon volunteers to help Scott with the radio and Pope making mech-killing ammunition. •
Seychelle Gabriel as Lourdes, a former first year medical student who assists Anne. She is religious, and her faith is still strong despite the circumstances. She has a crush on Hal, discouraged by Karen. •
Peter Shinkoda as Dai, a fighter. Dai had no family to lose in the invasion, so seeing Tom as worrying parent, he counts his blessings. •
Mpho Koaho as Anthony, a former Boston cop who is a fighter in the 2nd Mass and part of Tom's team. •
Connor Jessup as Ben Mason, Tom's 14-year-old second son who was captured by the Skitters. In the pilot, Hal saw Ben among children wearing spinal harnesses, controlled by Skitters. He is eventually rescued and the harness removed, but the chemical changes, including strength and energy, and can hear radio waves[an ability used to hold off skitters and Mechs]. •
Will Patton as Dan Weaver, the commander of the 2nd Mass. Weaver is a retired active and reserve military officer with the rank of captain, who served with Porter during the
Gulf War. He does not like that the 2nd Mass includes so many civilians, but recognizes their role in giving fighters hope. He believes his family is lost, but finds evidence his wife and eldest daughter survived. Weaver was religious, but lost faith when the aliens came. •
Sarah Carter as Margaret ("Maggie"), was coerced and raped by Pope's team, so willingly helped Tom's squad escape. She wants to earn a place in the 2nd Mass. She knows opiate drug sources and the hospital where Skitters keep harnessed children because she had "bad" cancer at 16. •
Colin Cunningham as John Pope, the leader of a post-apocalyptic gang. He captured Tom, Hal, Karen, Anthony, and Dai and intended to trade them back to the 2nd Mass in exchange for an
M2 Browning. Pope was captured and the rest of his gang killed when the alien ship shot at their flares.
Recurring •
Bruce Gray as Scott, Anne's uncle, teaches kids biology and repairs an old tube radio that detects Skitters communicating. •
Dylan Authors as Jimmy Boland, a 13-year-old soldier who fights in the 2nd Mass. • Daniyah Ysrayl as Rick, son of Mike. He was harnessed by the Skitters. • Martin Roach as Mike Thompson, a soldier for the 2nd Mass. His son was captured by the aliens. He was killed in Sanctuary Part 2 by Terry Clayton who took children, including all from 2nd Mass, for the Skitters. •
Dale Dye as Colonel Porter, the leader of the resistance against the Skitters in Boston. He was a U.S. military officer on the verge of retirement when the invasion came. •
Steven Weber as Michael Harris, a medical surgeon was friends with Tom and his wife, until he left her to attacking aliens. He finds the procedure to cut away harnesses with a blowtorch, leaving spikes, and medicate heavily with opiates to reduce withdrawal from harness-injected chemicals. He is killed while trying to inject a wounded Skitter brought back by Tom. • Lynne Deragon as Aunt Kate, Anne's aunt and Scott's wife. • Melissa Kramer as Sarah, a pregnant civilian in 2nd Mass. • Henry Czerny as Terry Clayton • Brent Jones as Click == Episodes ==