Billionaire entrepreneur Richard Branson has vowed to fight for the next 40 days to save the life of a US death row inmate whose execution was postponed at the last minute.

A US man on death row in Oklahoma who has been granted a last minute stay of execution has said he is happy to have 37 more days.

Update at 11pm: The execution of death row prisoner Richard Glossip in Oklahoma has been halted after the State's governor stepped in. Mary Fallin has issued a 37-day stay of execution to address legal questions about Oklahoma's execution protocols and the chemicals used for lethal injection.

The execution of an American man for a murder he says he played no part in, has been dramatically halted.