"He's a bit older but more experienced and I look back at how well David Weir and Alan Stubbs did for us in their 30s, and I hope Sylvain can do the same.
"We need someone to come in and keep us steady because we want to be competing be at the top end of the Premier League."
Distin is Moyes's third major capture of the current transfer window, following on-loan striker Jo and Russia international midfielder Diniyar Bilyaletdinov.
Distin could come straight into the team for Sunday's home clash against Wigan despite not training with his new team-mates on Friday.
He added: "I did think about it, but not for too long. It is important to move to a club looking up not down.
"In my first season at Portsmouth we won the FA Cup and with the kind of players we were signing at the time everyone expected it to carry on.
"But it went in the opposite direction. It was really difficult last year and this season the club is also in a tough situation.
"So it was not enjoyable, but those things happen in football."
Pompey had been linked with a move for Manchester City's Richard Dunne, but he now appears set to join Aston Villa.
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