Armet Francis was born in St Elizabeth, in rural Jamaica in 1945. He was left in the care of his grandparents at the age of three when his parents moved to London, where Francis joined them seven years later in 1955.Interviewed for the British Library's Oral History of British Photography, Francis spoke of growing up as the only black child in a school in London Docklands. After leaving school at 14, he worked for an engineering firm in Bromley, before finding a job as an assistant in a West End photographic studio, and going on to forge a career as freelance photographer for fashion magazines and advertising campaigns.

He has said: "In 1969 I embarked on a lifetime project.... I was living and working in the first world, materially that is, but becoming more aware of inequalities to the third world, to be more specific the Black World. As a Black photographer I started to realise I had no social documentary images in my work.... I went back [to Jamaica] in 1969.... I had been away 14 years, it would take another 14 years to make sense of this project." Following his participation at Festac '77 (the Second World Black and African Festival of Arts and Culture) in Lagos, Nigeria, he became devoted to photographing the people of the African diaspora.

He became the first Black photographer to have a solo exhibition at The Photographers' Gallery in London when The Black Triangle series was exhibited there in 1983. He published a book also entitled The Black Triangle the following year, and Children of the Black Triangle was produced four years later. He was a contributing photographer in the survey issue of Ten. 8 vol. 2, no. 3, 1992, titled Critical Decade: Black British Photography in the 80s.

In 1988 Francis was a co-founder of the Association of Black Photographers (now Autograph ABP). He was the official photographer for Africa '05, a major celebration of African arts held throughout 2005 in the UK. Francis was one of three pioneering Jamaican-born photographers – the others being Charlie Phillips and Neil Kenlock – whose work was showcased in the 2005/2006 exhibition Roots to Reckoning at the Museum of London, which in 2009 with the assistance of Art Fund acquired the "Roots to Reckoning archive", comprising 90 photographs of London's black community from the 1960s to the 1980s.

The British Library conducted an oral history interview (C459/214) with Armet Francis in 2013 for its Oral History of British Photography collection.

Photographs by Francis featured prominently in Staying Power, the collaborative project mounted in 2015 by the Victoria and Albert Museum (V&A) and the Black Cultural Archives. "The arresting first image in the V&A museum is Jamaican photographer Armet Francis's Self-portrait in Mirror (1964), a curiously intimate and honest image showing Armet setting up his shot directly in front of a mirror," noted the reviewer for Culture Whisper, while Brennavan Sritharan commented in the British Journal of Photography: "Self-portraiture is something of a sub-theme, with Armet Francis' tender yet assertive self-portrait leading the exhibit."

In February 2022, Francis was named in CasildART's list of the top six Black British photographers, alongside Charlie Phillips, James Barnor, Neil Kenlock, Pogus Caesar and Vanley Burke.