He was a key cabinet member in the Ukrainian government (backed by Stepan Bandera's faction of OUN), which proclaimed independence on 30 June 1941.

He was assassinated on 12 October 1957 in Munich by a KGB agent, Bohdan Stashynsky, using a hydrogen cyanide atomizer mist gun.

Explaining what motivated him to kill Rebet, Stashynsky told a court that he had been told that Rebet was "the leading theorist of the Ukrainians in exile," since "in his newspapers Suchasna Ukrayina (Contemporary Ukraine), Chas (Time), and Ukrayinska Trybuna (Ukrainian Tribune) he not so much provided accounts of daily events as developed primarily ideological issues."

According to West German Intelligence chief Reinhard Gehlen, ...Bohdan Stashinskyi, who had been persuaded by his German-born wife Inge to confess to the crimes and take the load off his troubled conscience, stuck resolutely to his statements.

He reconstructed the crimes exactly as they had happened, revisiting the crumbling business premises at the Stachus, in the heart of Munich, where Lev Rebet had entered the office of a Ukrainian exile newspaper, his suitcase in his hand.

He served most of it and was released...[9]In 1984, Associated Press reported that Bohdan and Inge Stashinsky had been given new identities and had been provided asylum by the Government of South Africa.