Frank was a member of the Communist League, the French Trotskyist organisation, in the 1930s. he was a part of the faction within the movement led by Pierre Molinier and was a member of the groups formed by Molinier.
When the Second World War broke out Frank was sent to Britain in order to continue legally publishing the movements documents. He issued a publication called International Correspondence but as an illegal resident was briefly imprisoned. Apart from the help of Betty Hamilton the British Trotskyists were not in sympathy with his views.
At the end of WW2 he returned to France and joined the leadership of the Internationalist Communist Party (PCI). Generally he was supportive of the positions put forward by the international leadership around Mandel and Pablo supported by the American SWP.
He was important in maintaining the PCI in the 1950s and into the 1960s. When the PCI was dissolved into the new Communist League in 1968 he was a part of the leadership and continued in it until his death.
he was the author of a history of Trotskyism entitled The Long March of the Trotskyists.