An Iranian asylum seeker who has been declared brain dead in Brisbane will help save lives in the country he never reached after a family decision to donate his organs, according to refugee advocates.

Hamid Kehazaei, 24, was on life-support in Brisbane's Mater Hospital as about 40 supporters held a lunchtime vigil outside on Thursday.

Mark Gillespie from the Refugee Action Collective said Mr Kehazaei's family, who were not in Australia, had given the go-ahead for his organs to be donated once his life-support had been switched off.

"It's extremely distressing just trying to understand what has happened, although they recognise Hamid's life is terminal," he said.