Baker played the Doctor for seven consecutive seasons, making him the longest-serving actor in the part, and his incarnation is often regarded as the most popular of the Doctors. According to BBC News in 2006, in polls conducted by Doctor Who Magazine, Baker had only lost the "Best Doctor" category to Sylvester McCoy in 1990 and to David Tennant in 2006. In a 2010 interview, Baker said that he had not watched Tennant's performance as the Doctor but thought his Hamlet was excellent. Many of the stories from his early period are considered to be classics of the series, including The Ark in Space (1975), Genesis of the Daleks (1975), The Brain of Morbius (1976), The Deadly Assassin (1976) and The Robots of Death (1977). However, the violent tone of the stories produced by Philip Hinchcliffe saw the series come under heavy criticism from morality campaigner Mary Whitehouse. Concerns over violence during this early period led to a lightening of the tone and an "erratic decline" in both the popularity and quality of the series. In a 2014 interview, Baker described Hinchcliffe as "amazing" and identified that as his favourite period of his time on the series. He described Hinchcliffe's successor, Graham Williams, as "absolutely devoted" but lacking his predecessor's flair and "let me get away with murder". He acknowledged that his final producer on the series, John Nathan-Turner, made changes he did not agree with and they "did not see eye-to-eye really about very much"; however, according to Baker, the two became good friends afterwards and forgot their disagreements. Baker additionally criticised season 18, his last on the show and Nathan-Turner's first as producer, for an increase in the regular cast, which resulted in what Baker saw as stories that were excessively reliant on the Doctor (rather than other principal characters) to drive the plot forward. Baker ultimately suggested that he may have stayed in the role for one series too many, stating in hindsight that he felt it would have been better for him to have left with Williams and let Nathan-Turner recast the role of the Doctor for season 18.
Baker is a prolific voiceover artist and his voice was voted as the fourth most recognisable in the UK in 2006 after the Queen, Tony Blair and Margaret Thatcher. In 1992 and 1993, Baker narrated BBC radio comedy series Lionel Nimrod's Inexplicable World. In 1994 he provided the narration for Channel 4's Equinox rave documentary Rave New World. In 2002 he had a speaking role in the critically acclaimed but commercially unsuccessful Hostile Waters as the Narrator.
Baker provided the voiceover for the Perfect Dark (2000) TV adverts. He also voiced both the narrator and the god "Tetsu" in the role-playing game Sudeki, but was uncredited. During the first three months of 2006, his voice was used by BT for spoken delivery of text messages to landline phones. He recorded 11,593 phrases, containing every sound in the English language, for use by the text-to-speech service. The BT text message service returned from 1 December 2006 until 8 January 2007, with two pence from each text going to the charity Shelter. Also, a single "sung" by Baker's text voice, "You Really Got Me" by The Kinks, was released on 18 December 2006 with proceeds going to the charity. The creator of the song was Mark Murphy, designer of the site.