Action thriller author Mr McNab has set up a petition to try to help homeless former SAS Sergeant Bob Curry.
Mr Curry, 64, played a crucial part in the 1980 operation to free hostages held in the London embassy building by terrorists.
But after his business failed he was forced to sleep in B&B hostels and on his daughter’s sofa after the local council failed to re-house him.
Mr McNab, 58, has demanded that Herefordshire County Council find a “suitable permanent property” for Mr Curry.
More than 14,000 people have signed a petition urging the council to help the “hero who has repeatedly put his life on the line for his country”.
Mr Curry said: “If this can happen to me, it can happen to any veteran and it is happening to veterans all over the country.”
He won the nickname “Backdoor Bob” by breaking into the rear of the Kensington embassy with a sledgehammer so the SAS team could swarm in.
Five of the six terrorist gunmen were killed and all except one of the hostages freed.
In an exemplary career, Mr Curry also served in Northern Ireland and the Falklands.
But three years ago he was forced to sell his SAS beret, belt and badge to a collector for £24,000.
He claimed the council offered him a hostel place but the accommodation was unbearable so he slept in his daughter’s living room instead.
“It was as if the society I had fought for all my life had turned its back on me,” he said.
A council spokesman said it was continuing to work with Mr Curry to help him to “secure appropriate housing”.