McGarvey hails from Armagh, Northern Ireland, and began his career as a stills Photographer before attending film school at the University of Westminster in London. Upon graduating in 1988, he began shooting short films and documentaries, including Skin, which was nominated for a Royal Television Society Cinematography Award, and Atlantic, directed by Sam Taylor-Wood. The latter project, an experimental, three-screen projected film created in 1997, earned Taylor-Wood a nomination for the 1998 Turner Prize, and would lead to an ongoing collaboration between McGarvey and the Director.

McGarvey has also won three Evening Standard British Film Awards for Atonement, Anna Karenina and Stephen Daldry's The Hours; and a quartet of Irish Film & Television Awards for Atonement, Anna Karenina, Sahara and We Need to Talk About Kevin. In 2004, he was awarded the Royal Photographic Society's prestigious Lumiere Medal, sharing the company of such pioneers as Jack Cardiff, Freddie Francis, Roger Deakins and Ridley Scott, for contributions to the art of cinematography.

He has collected two Academy Award nominations for his cinematography on Joe Wright's 2007 drama, Atonement and his 2012 adaptation of Leo Tolstoy's classic novel Anna Karenina.

He reunited with Director Wright for his 2009 drama The Soloist, and filmmaker Sam Taylor-Wood (now Sam Taylor-Johnson) on her acclaimed 2008 drama, Nowhere Boy, her 2011 short, James Bond Supports International Women's Dayand the Death Valley segment of the 2006 erotic drama Destricted. Following his work on Godzilla, he reteamed with Taylor-Johnson on her big screen adaptation, and Hollywood directorial debut, of the bestselling novel Fifty Shades of Grey.

His four dozen credits as Director of photography include Joss Whedon's superhero film The Avengers, the industry record holder for highest opening weekend box office upon its release in May 2012; Lynne Ramsay's We Need to Talk About Kevin; Oliver Stone's World Trade Center; Gary Winick's Charlotte's Web; John Hamburg's Along Came Polly; Stephen Frears' High Fidelity; Mike Nichols' Wit; Michael Apted's Enigma; Michael Winterbottom's Butterfly Kiss, McGarvey’s first feature film credit; and two projects marking actors' directorial debuts: Tim Roth's The War Zone and Alan Rickman's The Winter Guest. He also served as Cinematographer on the pilot for the BBC/HBO TV series The No. 1 Ladies Detective Agency, directed by Anthony Minghella.

In 2015, he was awarded an Honorary Doctor of Laws from Dundee University and an Honorary Doctor of Fine Arts from the University of Ulster. He is also an Honorary Fellow of Edinburgh College of Art.