Kersten was born in a Baltic German family in Estonia when the country was still a part of Imperial Russia. During World War I he fought in the German Army and arrived in Finland in April 1918 with the German forces that intervened in the Finnish Civil War. Kersten served for a while in Suojeluskunta, was granted Finnish citizenship in 1920 and commissioned 2nd Lieutenant (vänrikki) in the Finnish Army in September 1921.

Kersten began his studies in Helsinki where he studied with the specialist Dr Colander. After two years' study he was awarded his degree in scientific massage. He then left for Berlin where he continued his studies and eventually became Dr. Ko's pupil after an encounter at a dinner party. In 1925 Dr. Ko told Kersten "You have learned all I can teach you." He then turned his patients over to Kersten and retired.

Kersten had a number of very influential customers, among them prince Hendrik of the Netherlands (since 1928) and Mussolini’s son-in-law and Foreign Minister Galeazzo Ciano. Kersten felt he had to fulfill Heinrich Himmler's request to become Himmler's personal masseur. He wrote that he feared for his safety in case he refused. Kersten was able to alleviate Himmler’s severe stomach pains with his skills, and retained Himmler's trust until the end of the World War II in 1945.

He was able to alleviate Himmler’s severe stomach pains with his skills and gained his trust. Kersten used this trust to obtain pardons and releases of several prisoners.

During the War, Kersten also provided information to the OSS (predecessor of the CIA).

Towards the end of the War, Kersten arranged a meeting with Himmler and Norbert Masur, a member of the Swedish branch of the World Jewish Congress, in Harztwalde, a few miles from Ravensbrück concentration camp. As a result Himmler agreed to spare the lives of the remaining 60,000 Jews left in Nazi concentration camps days before their liberation by the Allies.

In December 1945 the World Jewish Congress presented Kersten with a letter thanking him for helping to save Jewish concentration-camp victims.

In his post-war memoirs Kersten takes credit for saving, among others, the whole Dutch people from forced deportation to the Nazi-occupied East. Even if some of his claims are unverifiable, they are not entirely baseless. Although the details of Kersten’s activities are hard to discern, at least the Dutch government thought highly enough of Kersten to nominate him In 1953 for the Nobel Peace Prize on this account.

However a later official Dutch investigation concluded that no such plan had ever existed and that some of Kersten's documents were fabricated.

The Swedish archives testify that Kersten was intermediary between Himmler and Count Folke Bernadotte in the negotiations which led to the rescue operation "The White Buses", saving hundreds of Norwegians and Danes from certain death in the last days of the Third Reich. Kersten’s claims of being instrumental in saving Finland’s Jews from German hands might be exaggerated, but Finnish government did use his services in hope of influencing Himmler.

After the war Kersten lived in West Germany and Sweden, taking Swedish citizenship in 1953. Kersten's war memoirs were published in English translation the first time in 1947, and in a second edition in 1956 (The Kersten Memoirs, 1940-1945, London 1956) with an introduction by H. R. Trevor-Roper.

Examining the story of Felix Kersten, the doctor to Heinrich Himmler who used his position to save potentially thousands of people from Nazi persecution during the Second World War.