Robert Guy Bathurst was born in Accra, Gold Coast (modern-day Ghana), on 22 February 1957 to Philip Charles Metcalfe Bathurst, a descendant of Politician Charles Bathurst and kinsman of the Earls Bathurst and Viscounts Bledisloe, and his wife Gillian (née Debenham). His father was a major in the Royal Engineers during the Second World War and was working in West Africa as a management consultant. His mother was a physiotherapist. They had two other children, Nicholas and Charlotte. The family lived in Ghana until 1959, when they moved to Ballybrack]], Dublin, Ireland. Bathurst and his brother attended two schools in Dublin – the Holy Child School in Killiney and a school in Ballsbridge – before being sent to a preparatory school in Kells, County Meath. He compared the time he and his brother, who were Catholics, spent at the Anglican boarding school to Lord of the Flies; "we were incarcerated in a huge, stinking, Georgian house, where we were treated very brutally".

In 1966, the family moved to England. Bathurst transferred to the Worth Abbey boarding school in Sussex, which he much preferred to the school in Kells. At the age of 13, he began acting in minor skits and revues and read old copies of Plays and Players magazine, "studying floor plans of theatres and reading about new theatres being built". He had first become interested in acting when his family saw a pantomime at the Gaiety Theatre in Dublin and he watched actors waiting for their cues in the wings.

Bathurst left Worth at the age of 18 to read law at Pembroke College, Cambridge. Describing himself as "hopeless at anything academic", He spent much of his time there performing in the Cambridge Footlights alongside Hugh Laurie, Rory McGrath and Emma Thompson. From 1977 to 1978, he was the secretary of the group and from 1978 to 1979, he was the President. Among the Footlights Revues in which he participated were Stage Fright in 1978, which he also co-wrote and Nightcap in 1979. He also directed and appeared in the Footlights pantomime Aladdin as Widow Twankey during the 1978–79 season. He took the Bar Vocational Course at the University of Law, in London, which allowed him to go on to become a practising barrister, but stuck to acting instead.

He continued to make minor appearances in television throughout the 1980s; in 1987, he auditioned for the role of Dave Lister in the BBC North science fiction sitcom Red Dwarf. The part eventually went to Craig Charles but Bathurst was given a role in the first episode of the first series as Frank Todhunter, second officer on the ship, who is killed in the first ten minutes. Ten years later, Bathurst was invited to reprise the role when a storyline in the series allowed former characters to return, but filming commitments prevented him from appearing. In 1989, he appeared in Malcolm Bradbury's Anything More Would Be Greedy for Anglia Television, playing Dennis Medlam, MP. The programme was broadcast in 1990 to little fanfare. In 1990, he performed on Up Yer News, a live topical programme broadcast on BSB.

After leaving Cambridge, Bathurst spent a year touring Australia in the Footlights Revue Botham, The Musical, which he described as "a bunch of callow youths flying round doing press conferences and chat shows". Although he enjoyed his work with Footlights, he did not continue performing with the group, worrying that he would be "washed up at 35 having coat-tailed on their success through the early part of [his] career". After leaving, he found that he was considered a dilettante, which resulted in it taking him longer than expected to be accepted as a serious actor. His first professional role out of university was in the BBC Radio 4 series Injury Time, alongside fellow Footlights performers Rory McGrath and Emma Thompson. His first role for television came in 1982, when he appeared as Prince Henry in the unaired pilot episode of Blackadder. He had already appeared in a training video by Director Geoff Posner and got the role of Henry by way of thanks. The character was recast and downgraded when the series was commissioned as The Black Adder.

He made his professional stage debut in 1983, playing Tim Allgood in Michael Frayn's Noises Off, which ran for a year at the Savoy Theatre. To broaden his knowledge of working on stage, he joined the National Theatre. He supplemented his stage roles in the 1980s with television roles, appearing in comedies such as the aborted pilot episode of Blackadder, Chelmsford 123, The Lenny Henry Show and the first episode of Red Dwarf. In 1991, he won his first major television role playing Mark Taylor in Steven Moffat's semi-autobiographical BBC sitcom Joking Apart. Although only thirteen episodes were made between 1991 and 1995, the role remains Bathurst's favourite of his whole career. After Joking Apart concluded, he was cast as pompous management consultant David Marsden in the ITV comedy drama Cold Feet, which ran for five series from 1998 to 2003.

Bathurst's professional stage debut came the next year when he joined the second cast of Michael Frayn's Noises Off at the Savoy Theatre. He replaced Roger Lloyd-Pack as Tim Allgood and stayed at the Savoy for a year. Between roles, he worked as a television presenter for BBC East. After declining an offer to be a presenter of That's Life! he joined the National Theatre in 1984, where he appeared as a background actor in Saint Joan. He regards it as "the most demoralising" job he has ever had but was grateful for the theatre experience it gave him. The following year, he appeared at The Man In The Moon, a pub theatre in Chelsea, in Judgement, a two-hour monologue on cannibalism. The opening night audience was made up of three people but after good reviews in the national press the audience grew to an average of fifteen.

Bathurst met Artist Victoria Threlfall through mutual friends and they married in 1985. They have four daughters: Matilda, Clemency, Oriel and Honor.

Between 1991 and 1995, Bathurst also appeared on television in No Job for a Lady, The House of Eliott and The Detectives and on stage in The Choice, George Bernard Shaw's Getting Married at Chichester with Dorothy Tutin and Gogol's The Nose adapted by Alastair Beaton, which played in Nottingham and Bucharest. He also filmed a role in The Wind in the Willows (Terry Jones, 1996) as St John Weasel.

While working on Up Yer News, Bathurst auditioned for a one-off television comedy called Joking Apart. Earlier in the day, he noticed a fellow Up Yer News performer reading the script to prepare for his own audition. As Bathurst went into the audition room, his colleague was leaving and told Bathurst he would "break his legs" if he got the part, a threat that seemed not to be "entirely jocular". Bathurst got the part and the pilot of Joking Apart was broadcast as an installment of the BBC 2 Comic Asides strand. It returned for two series in 1993 and 1995. Bathurst appeared as sitcom Writer Mark Taylor in the series. After the first series was broadcast, a critic called Bathurst the "Best Comedy Newcomer of 1993".

In 1996, while appearing in The Rover at the Salisbury Playhouse, Bathurst got an audition for the Granada Television comedy pilot Cold Feet. He arrived for the audition "bearded and shaggy", on account of his role in the play and did not expect to win the role of upper-middle class management consultant David Marsden. The role in the pilot was only minor and created at the last minute to support characters played by James Nesbitt and Helen Baxendale; the only character note in the script about David related to his high salary. Bathurst identified the character as merely a "post-Thatcherite whipping boy".

Between 1998 and 2003, he made television appearances in Goodbye, Mr Steadman (2001), starring opposite Caroline Quentin as a headmaster who has been declared dead after one of his pupils erases all computer records relating to him and in the adaptation of White Teeth (2002). On stage, in 1998 he appeared in Michael Frayn's Alarms and Excursions and in 1999 in Hedda Gabler, which was his last theatre role for several years. In the Daily Telegraph, Charles Spencer described his role as Tesman as a "weird casting choice" but called his acting "a brave stab". In 2001, Bathurst appeared in the music video for Westlife's Comic Relief single "Uptown Girl".

In 2002, straight after finishing Cold Feet, Bathurst went straight into filming My Dad's the Prime Minister, a series in which he portrays fictional British prime minister Michael Philips. The first series was broadcast in a Sunday afternoon CBBC slot in 2003. He watched debates in the House of Commons to prepare for the role but did not base his portrayal on Tony Blair. In 2003, he returned to theatre for the first time in four years to play Vershinin in The Three Sisters, opposite Kristin Scott Thomas and Eric Sykes. He had not seen The Three Sisters before starring in it. Director Michael Blakemore advised him to turn this to his advantage, as he would not feel he had to live up to previous portrayals. After its run concluded, a special edition of The Three Sisters was filmed with the same cast for television broadcast on BBC Four. In 2005, the second series of My Dad's the Prime Minister was broadcast, now moved to a Friday night time slot to take advantage of the adult humour. The same year, he starred in the ITV thriller The Stepfather playing Christopher Veazey, a man whose daughter goes missing. Bathurst was pleased that this white-collar worker had an emotional side, in comparison to David Marsden, whom he used as a yardstick when accepting those sorts of roles. Also in 2005, he played Mr Sesseman in an adaptation of Heidi and Dottore Massimo in The Thief Lord.

Since 2003, Bathurst has played a fictional prime minister in the BBC sitcom My Dad's the Prime Minister, Mark Thatcher in the fact-based drama Coup! and a man whose daughter goes missing in the ITV thriller The Stepfather. He also made a return to theatre roles, playing Vershinin in The Three Sisters (2003), Adrien in the two-hander Members Only (2006), government whip Alistair in Whipping it Up (2006–07), and Alex in Alex (2007, 2008). In the following years he starred in the television dramas The Pillars of the Earth (2010), Downton Abbey (2010), Hattie (2011) and joined the cast of Wild at Heart in 2012. Bathurst appeared in his first Noël Coward play, Present Laughter in 2010 and followed it with a role in Blithe Spirit in 2010 and 2011. He is married and has four children.

After a season at the Bush Theatre at the end of 2006, Whipping it Up transferred to the New Ambassadors Theatre from March to June 2007. The tour coincided with his appearance as the titular character in Alex, based on the comic in The Daily Telegraph. The play ran at the Arts Theatre between October and November 2007 and featured Bathurst interacting with other characters projected onto a screen behind him. He was attracted to the role because of the "duplicity and guile" Alex uses to get himself out of tight situations. The role won him a nomination for Best Solo Performance at the What's on Stage Awards. He reprised the role in an international tour from September to November 2008, playing in Melbourne, Sydney, Hong Kong, Singapore and Dubai. As Alex he presented a ten-part series on Classic FM, which won a Gold Award at the Sony Radio Academy Awards in 2012. He now performs Alex as a corporate after-dinner entertainment. 2007 also saw Bathurst perform as Linguist Charles in the first series of the BBC Radio 4 sitcom Hut 33. He reprised the role for two more series in 2008 and 2009.

In 2009, he made his third and final appearance as art dealer James Garrett in My Family. He also played the role of Mr Weston in the BBC costume drama Emma, which was broadcast in October 2009 on BBC One. He previously played Weston in a two-part adaptation of Emma for BBC Radio 4 in 2000. Between January and April 2010, Bathurst starred as Garry Essendine in a national touring revival of Noël Coward's Present Laughter. He had not seen Present Laughter before, though had seen several Coward plays in his 20s and did not imitate Coward's speech patterns while performing. Present Laughter was the first time Bathurst had appeared in a Coward play and he was cast in another, Blithe Spirit, later in the year. He plays Charles Condomine opposite Alison Steadman and his Cold Feet co-star Hermione Norris. The play toured theatres around southern England in 2010 and early 2011 before beginning a three-month run at the Apollo Theatre in London.

On television in 2010, Bathurst starred as Percy Hamleigh in the German-Canadian miniseries The Pillars of the Earth and had a recurring role as widower Sir Anthony Strallan in the period drama Downton Abbey. In 2011 he starred as John Le Mesurier in the Hattie Jacques biopic Hattie, and joined the cast of the long-running ITV drama Wild at Heart.

A casting Director for the James Bond film The Living Daylights persuaded Bathurst to audition for Bond. Bathurst believes that his "ludicrous audition" was only "an arm-twisting exercise" because the producers wanted to pressure Timothy Dalton to take the role by telling him they were still auditioning other actors. Bathurst noted "I could never have done it – Bond actors are always very different from me".

In September 2016, Bathurst reprised his role of David Marsden in Cold Feet.