[2] In 1979 he left the Royal Court Theatre and began writing and directing as a freelance, the most successful result of which was Private Dick, a comedy about Raymond Chandler co-written with Richard Maher, which opened at the Lyric Hammersmith to great reviews, and later moved to the West End with Robert Powell as Philip Marlowe.

Subsequently, his first piece of television was the three-part Leigh Jackson thriller Downtown Lagos, produced by Michael Wearing, which in turn led to the award-winning adaptation of Hanif Kureishi's autobiographical novel The Buddha of Suburbia, starring Naveen Andrews, which he scripted with the novelist.

Throughout the 1990s, Michell directed a number of productions at the National Theatre including Mustapha Matura's The Coup, Pinter's The Homecoming, Dylan Thomas’s Under Milk Wood, Joanna Murray Smith's Honour, Joe Penhall's Landscape With Weapon, Granville Barker's Waste, Nina Raine's Consent (subsequently at the Harold Pinter Theatre in the West End), and Blue/Orange with Bill Nighy, Andrew Lincoln, and Chiwetel Ejiofor, which won numerous awards and played in the West End for a year.

Michell was subsequently sought out by Richard Curtis to direct his script Notting Hill, which became an award-winning smash hit and the greatest British Box Office success of all time.

[3] For the next decade, Michell chose for personal reasons to work only in the UK, and in 2003 directed The Mother, his second collaboration with Hanif Kureishi, starring Anne Reid and Daniel Craig.

Michell was in negotiations to work with Craig yet again in 2006 on what became the James Bond film Quantum of Solace, but after months of unfruitful script conferences, and in spite of good relationships with the producers, he jumped ship.

After working with Ellie Goulding on the mini rom-com How Long Will I Love You?, Michell directed the much-lauded two-part TV drama The Lost Honour of Christopher Jefferies, written by Peter Morgan, and telling the true-life story of a retired schoolteacher accused of murder.

Next came his own adaptation of Daphne du Maurier's novel My Cousin Rachel, starring Sam Claflin and Rachel Weisz; the acclaimed documentary Nothing Like a Dame for the BBC, featuring Joan Plowright, Maggie Smith, Eileen Atkins, and Judi Dench; the euthanasia-focused family drama Blackbird with Kate Winslet, Sam Neill, Susan Sarandon, Rainn Wilson, Mia Wasikowska, and Lindsay Duncan; and The Duke, with Helen Mirren and Jim Broadbent, which premiered to universal acclaim at the 2020 Venice Film Festival.