Whately lives in Woburn Sands near Milton Keynes with his wife Actress Madelaine Newton, who starred in the 1970s BBC drama When the Boat Comes In. Madelaine starred as Morse's love interest in the Inspector Morse episode entitled Masonic Mysteries (1990; series 4, episode 4).

Whately was educated at Barnard Castle School, and went on to study drama at the Central School of Speech and Drama in 1975. Before going professional, Whately was an amateur actor at the People's Theatre in Newcastle upon Tyne during the 1970s. His brother, Frank, is a drama lecturer at a London university.

Richard Marson's book celebrating fifty years of Blue Peter comments that Whately auditioned as a presenter for the show in 1980 but lost out to Peter Duncan.

In 1985, Whately appeared in a 3-part Miss Marple adaptation ("A Murder Is Announced") for the BBC. His part, Detective Sergeant Fletcher, opposite John Castle as Inspector Craddock, was very similar to what became the career-defining role he took two years later, when he was cast as Detective Sergeant Lewis, the down-to-earth complement to the eponymous Inspector Morse played by John Thaw. Whately starred opposite Thaw in 32 episodes over 13 years in the hugely successful series that established him as a household name in the UK.

Whately enjoys rock music and plays the guitar; he has cited Pink Floyd and Dire Straits as bands he has particularly enjoyed. He is a fan of Newcastle United on the football field, but says that he likes rugby league better, and as a cricketer admitted to Inspector Morse Writer Colin Dexter that he would like to have played cricket professionally for England. Dexter devised the storyline for the Inspector Morse episode "Deceived by Flight" (1989; series 3, episode 3) in which Sergeant Lewis had to go undercover in a cricket team to investigate drug smuggling.

Whately's television appearances include episodes of Shoestring, Angels, Juliet Bravo, Strangers, Coronation Street, Auf Wiedersehen, Pet, Alas Smith and Jones, Look and Read, You Must Be The Husband, B&B, Peak Practice, Skallagrigg, The Broker's Man, Murder in Mind, Inspector Morse, 2003 Comic Relief Auf Wiedersehen, Pet, Lewis, New Tricks, Who Gets the Dog?, The Children and Silent Cry. Whately provided one of the voices for the English-language version of the 1999 claymation Children's television series Hilltop Hospital. He has also done voiceovers for a WaterAid advertisement.

Whately is from Humshaugh, near Hexham, Northumberland. His mother, Mary (née Pickering), was a Teacher and his father, Richard, was a Commander in the Royal Navy. His maternal grandmother, Doris Phillips, was a professional concert singer and his great-great-grandfather, Richard Whately, was Anglican Archbishop of Dublin. The BBC documentary Who Do You Think You Are?, broadcast on 2 March 2009, also revealed that Whately is a descendant, on his paternal side, of Thomas Whately of Nonsuch Park, a leading London merchant, English Politician and Writer who became a Director of the Bank of England, and of Major Robert Thompson, a pioneer tobacco plantation owner in Virginia who was a staunch supporter of the Parliamentarian cause at the time of the English Commonwealth.

In 2010 Whately played the lead in the television film Joe Maddison's War about strained family and social relations in wartime. Directed by Patrick Collerton, it presented a view of World War II through the eyes of shipyard worker and World War I veteran Joe Maddison (Kevin Whately) who serves in the Home Guard during the Blitz.

Whately was the patron of the Central School of Speech and Drama Full House Theatre Company for 2011.

Following the filming of the seventh series of Lewis, at the end of 2012, Whately and Laurence Fox announced that they would take a break of at least a year before filming more episodes. ITV indicated a continuing commitment to the series and that they wished to produce additional episodes of the programme. On 4 November 2012 Whately performed in a radio drama on BBC3 called The Torchbearers, which follows the circumstances of several UK citizens whose lives are changed through contact with the Olympic Torch. In 2013, Newcastle upon Tyne's Live Theatre produced a series of performances of the unique, acclaimed one-person play, White Rabbit, Red Rabbit, which is enacted as a cold reading with no sets or costumes by a different performer each night. Whately was the actor for the sold-out performance of 10 March 2013.

In August 2014, Whately was one of 200 public figures who were signatories to a letter to The Guardian expressing their hope that Scotland would vote to remain part of the United Kingdom in September's referendum on that issue.