Willem Oltmans was born in Huizen.

Against the will of the Dutch government, Oltmans interviewed Indonesian president Sukarno in 1956. In 1957 he pleaded for the transfer of New Guinea to Indonesia while in Indonesia. He claimed to have prevented a Dutch war against Indonesia over New Guinea by sending a memo to US president Kennedy. Since then Joseph Luns, minister of foreign affairs, covertly tried everything to sabotage Oltmans' career, with much success: for a long time, Oltmans was forced to live off welfare.

He fought a long law suit against the Dutch state, which he won. In 2000 a commission awarded him eight million guilders (four million dollars) in damages, after taxes. Having paid two million in lawyer's fees, Oltmans bought a penthouse on a canal in Amsterdam and a Steinway piano.

Oltmans was based in the USA in the 1960's, where he worked as a reporter for Dutch TV broadcaster NOS. After US president John Kennedy was assassinated in Dallas in 1963, Oltmans developed an alternative theory as to who was responsible for the murder. In his opinion, baron George de Mohrenschildt was the architect behind the killing. Ironically, Oltmans played de Mohrenschildt in Oliver Stone's 1991 film about the assassination, JFK.

He died in Amsterdam.