Motion was born in London and raised in Stisted near Braintree in Essex. After being sent, at the age of seven, to boarding school, was educated at Radley College. Here, in the sixth form, he encountered Mr Wray, an inspiring English teacher who introduced him to poetry – first Hardy, then Larkin, W H Auden, Heaney, Hughes, Wordsworth and Keats. When he was 17 years old, his mother had a riding accident and spent the next nine years in and out of a coma before dying. Motion has said that he wrote to keep his memory of his mother alive and she was a muse of his work. In the years that followed, he read English at University College, Oxford, where he studied with W. H. Auden in weekly sessions. Motion says “I worshipped him the other side of idolatry and it was like spending an hour each week in the presence of God.” He won the university's Newdigate Prize and graduated with a first class degree.

Between 1976–1980, Motion taught English at the University of Hull and while there, at age 24, he had his first volume of poetry published. At Hull he met university Librarian and poet Philip Larkin. Motion was later appointed as one of Larkin's literary executors which would privilege Motion's role as his biographer following Larkin's death in 1985. In Larkin: a writer's life, Motion says that at no time during their nine year friendship did they discuss writing his biography and it was Larkin's long time companion Monica Jones who requested it. He reports how, as executor, he rescued many of Larkin's papers from imminent destruction following his friend's death. His 1993 biography of Philip Larkin, which won the Whitbread Prize for Biography, was responsible for bringing about a substantial revision of Larkin's reputation.

Motion was Editorial Director and Poetry Editor at Chatto & Windus (1983–89), he edited the Poetry Society's Poetry Review from 1980–1982 and succeeded Malcolm Bradbury as Professor of Creative Writing at the University of East Anglia. In 2003, he became Professor of Creative Writing at Royal Holloway, University of London.

Twice married, he has two sons and one daughter and lives in Islington, north London.

Motion has said of himself: ‘My wish to write a poem is inseparable from my wish to explain something to myself’. His work combines lyrical and narrative aspects in a 'postmodern-romantic sensibility'.His an author's statement, Motion describes further the intention of his work:

My poems are the product of a relationship between a side of my mind which is conscious, alert, educated and manipulative, and a side which is as murky as a primaeval swamp. I can't predict when this relationship will flower. If I try to goad it into existence I merely engage with one side of my mind or the other, and the poem suffers. I want my writing to be as clear as water. No ornate language; very few obvious tricks. I want readers to be able to see all the way down through its surfaces into the swamp. I want them to feel they're in a world they thought they knew, but which turns out to be stranger, more charged, more disturbed than they realised. In truth, creating this world is a more theatrical operation than the writing admits, and it's this discretion about strong feeling, and strong feeling itself, which keeps drawing me back to the writers I most admire: Wordsworth, Edward Thomas, Philip Larkin.

The Independent describes the stalwart poet as the "charming and tireless defender of the art form". Motion has won the Arvon Prize, the John Llewellyn Rhys Prize, Eric Gregory Award, Whitbread Prize for Biography and the Dylan Thomas Prize.

Motion was appointed Poet Laureate on 1 May 1999, following the death of Ted Hughes, the previous incumbent. The Nobel Prize-winning Northern Irish poet and translator Seamus Heaney had ruled himself out for the post. Breaking with the tradition of the laureate retaining the post for life, Motion stipulated that he would stay for only ten years. The yearly stipend of £200 was increased to £5,000 and he received the customary butt of sack.

He wanted to write "poems about things in the news, and commissions from people or organisations involved with ordinary life," rather than be seen a 'courtier'. So, he wrote "for the TUC about liberty, about homelessness for the Salvation Army, about bullying for ChildLine, about the foot and mouth outbreak for the Today programme, about the Paddington rail disaster, the 11 September attacks and Harry Patch for the BBC, and more recently about shell shock for the charity Combat Stress, and climate change for the song cycle I've finished for Cambridge University with Peter Maxwell Davies." In 2003, Motion wrote Regime change, a poem in protest at Invasion of Iraq from the point of view of Death walking the streets during the conflict, and in 2005, Spring Wedding in honour of the wedding of the Prince of Wales to Camilla Parker Bowles. Commissioned to write in the honour of 109 year old Harry Patch, the last surviving 'Tommy' to have fought in World War I, Motion composed a five part poem, read and received by Patch at the Bishop's Palace in Wells in 2008. As laureate, he also founded the Poetry Archive an on-line library of historic and contemporary recordings of poets reciting their own work.

Motion remarked that he found some of the duties attendant to the post of poet laureate difficult and onerous and that the appointment had been "very, very damaging to [his] work". The appointment of Motion met with criticism from some quarters. As he prepared to stand down from the job, Motion published an article in The Guardian which concluded, "To have had 10 years working as laureate has been remarkable. Sometimes it's been remarkably difficult, the laureate has to take a lot of flak, one way or another. More often it has been remarkably fulfilling. I'm glad I did it, and I'm glad I'm giving it up – especially since I mean to continue working for poetry." Motion spent his last day as Poet Laureate holding a creative writing class at his alma mater, Radley College, before giving a poetry reading and thanking Peter Way, the man who taught him English at Radley, for making him who he was. Carol Ann Duffy succeeded him as Poet Laureate on 1 May 2009.