In a twist, the producers unveiled an unknown contestant, Chantelle, who must convince the others she is famous.
The Channel 4 show, now in its fourth series, is due to last 23 days.
Happy Mondays dancer Bez, Mark Owen and Jack Dee have previously won the show.
In Pictures: Celebrity Big Brother
Actress Rula Lenska, ex-Baywatch star Traci Bingham, pop star Pete Burns, from 1980s group Dead or Alive, Goldie Lookin' Chain rapper Maggot and Samuel Preston, lead singer of The Ordinary Boys, are the other contestants in the latest series.
"Just because the housemates are celebrities, doesn't mean that Big Brother isn't in charge or afraid to call the shots," said executive producer Sharon Powers.
Davina McCall will once again host the nightly show, which lasts three weeks.
Blair 'dilemma'
Before entering the house, teetotal Galloway, who is MP for Bethnal Green and Bow, said the show would be a "chance to show a large and different audience what I'm really like".
"Tony Blair will be in a dilemma. One part of him will want me to be evicted early so I don't score another victory," he said.
"On the other hand, as long as I'm in there, I'm leaving him alone. That's going to be a dilemma for those that don't like me .
It might take me back to where I am now, which would be devastating
Faria Alam
"Do they want me locked up in the Big Brother house, or do they want me at large and let loose on the streets?"
The inclusion of Michael Barrymore is controversial.
Once one of the highest-paid stars on TV before his fall from grace, Barrymore left the UK for New Zealand following the death at his home of Stuart Lubbock who drowned in his swimming pool.
He was dropped by ITV following an inquest, which recorded an open verdict, and he found it difficult to find work.
Mr Lubbock's family are angry at suggestions Barrymore could be paid £150,000 to take part in the show.
Barrymore said he had no "expectations" about whether the show would affect his career.
"If certain people want to call it a comeback," he said, "they can call it a comeback because I haven't been away."
And Alam said she hoped the show would allow people to get to know her.
"I am a good person. I'm not craving limelight," she said.
"I've got a hell of a lot riding on this. It might make me incredibly famous but it might not. It might take me back to where I am now, which would be devastating."