From 1980 until 1985, Franklin worked with Agence Presse Sygma in Paris. During that time he photographed the civil war in Lebanon, unemployment in Britain, famine in Sudan, and the Heysel Stadium disaster.
He joined Magnum Photos in 1985, and became a full member in 1989. In the same year, Franklin photographed the uprising in Tiananmen Square and shot one of the Tank Man photographs, first published in Time. That work, together with his documentation of the general uprising in Beijing, earned him a World Press Photo Award.
In 1989, Franklin traveled with Greenpeace to Antarctica. He worked on about 20 stories for National Geographic between 1991 and 2009; his subjects included Inca conqueror Francisco Pizarro, the hydro-struggle in Quebec, and places such as Buenos Aires and Malaysia. In addition, he worked on book and cultural projects. In October 2008, his book Footprint: Our Landscape in Flux was published by Thames & Hudson. An ominous photographic document of Europe's changing landscape, it highlights Franklin's deep ecological concern.
During 2009, Franklin curated an exhibition on Gaza—Point of No Return—for the Noorderlicht Photo Festival. Since 2009, Franklin has focused on a long-term landscape project in Norway, published as Narcissus in 2013. Recently Franklin has worked on documentary projects on doctors working in Syria, and immigration in Calais. Franklin's most recent book, The Documentary Impulse was published by Phaidon in April 2016. It investigates the nature of truth in reporting and the drive towards self-representation, beginning 50,000 years ago with cave art through various iterations and impulses that have guided documentary photography along its differing tracks for nearly 200 years. Franklin was the general chair of the World Press Photo jury in 2017.