After high school, Massimo dived straight into photojournalism, working first for a photo agency, before setting up his own agency, Massimo Sestini News Pictures, in 1984. He soon built up a client list that included major news publications such as Corriere della Sera and La Repubblica. He travelled the world, telephoto lenses in tow, hunting for scoops. The biggest of them came in the 1990s – he was the only photographer to cover the funeral of speedboat racer Stefano Casiraghi in 1990 and he took the first shot of Princess Diana in a bikini in 1991.
Alongside news, he's undertaken many public commissions, documenting the work of state institutions such as the police, the military and the fire service. In 2020, he exhibited Dante 700, a series commemorating the 700th anniversary of the famous Italian poet's death, at the Quirinal Palace in Rome. He also exhibited Indispensabili infermieri [Indispensable Nurses], a reportage about the role of nurses during the Covid-19 pandemic at Santa Maria Nuova Hospital and Palazzo Vecchio in his home town of Florence.