Thomas Brodie-Sangster was born in Southwark, a district in London, on 16 May 1990 to Mark Sangster and Tasha Bertram. Brodie-Sangster’s father’s family is from Banchory, Scotland. He has one sister. Brodie-Sangster plays bass and guitar, and he learned to play left-handed guitar to portray the left-handed Paul McCartney in the feature film Nowhere Boy. He also learned how to play the drums in the feature film Love Actually (2003).

In 2001, Brodie-Sangster’s first acting role was in a BBC television film, Station Jim. He subsequently appeared in a few more television films, including the lead roles in Bobbie’s Girl, The Miracle of the Cards (based on the story of Craig Shergold) and Stig of the Dump. He won the “Golden Nymph” award at the 43rd Annual Monte Carlo Television Festival for his role in the miniseries Entrusted. Brodie-Sangster’s first major theatrical film was Love Actually (2003), in which he played Sam. He was nominated for a Golden Satellite Award and a Young Artist Award for his role in the film.

Brodie-Sangster established Brodie Films in 2006 with his mother, Tasha Bertram, “to create opportunities in the film industry for new British talent; innovative writers, actors and directors.” The company was dissolved in May 2013.

In 2007, he appeared in a two-part story (Human Nature and The Family of Blood) in Doctor Who as schoolboy Timothy “Tim” Latimer, and guest-starred in the Big Finish Doctor Who audio dramas The Mind’s Eye and The Bride of Peladon. His voice lowered during filming of the Doctor Who episodes. He also starred in the film adaptation of Valerio Massimo Manfredi’s historical novel The Last Legion, released in 2007. That same year he voiced the character of Ferb Fletcher in the Disney Channel animated series Phineas and Ferb. He appeared in the 2008 miniseries Pinocchio, filmed in Italy, as Lampwick.

In 2008, Brodie-Sangster had a role in director Jane Campion’s film Bright Star, a love story about John Keats and his lover Fanny Brawne. He also starred as Paul McCartney in Nowhere Boy, a film directed by award-winning artist Sam Taylor-Wood, about the teenage years of John Lennon.

Brodie-Sangster plays bass guitar, and in January 2010 joined the band Winnet, in which his mother provides vocals.

Additionally, Brodie-Sangster plays Liam in the 2011 film The Last Furlong. In April 2011, he made a guest appearance as Adam Douglas in an episode of British detective drama Lewis. In 2012, he starred in The Baytown Outlaws and in Ella Jones’s short film, The Ugly Duckling, the third installment of the Tales trilogy of reworked fairy tales from More Films. From 2013 to 2014, he played the role of Jojen Reed in the HBO series Game of Thrones. In 2015, he began providing the voice of John Tracy in ITV’s remake of Gerry Anderson’s puppet series Thunderbirds Are Go (2015–present).

On 24 May 2017, a 15-minute sequel to Love Actually was released with Brodie-Sangster as part of the cast. It was shown on the BBC as part of Comic Relief’s Red Nose Day and titled Red Nose Day Actually and brought back a large number of characters from the first film.

In 2017, Brodie-Sangster began portraying Whitey Winn in the Netflix western drama miniseries Godless (2017).

He features in the 2020 Netflix miniseries The Queen’s Gambit as chess player Benny Watts.