"If I shine, if a really big club wants me, I know already that everything will go well.
"I am 22 and the most important thing for me is football - my job, my passion."
Diarra quickly became unsettled at Arsenal when he was often left on the fringes of the side.
The midfielder said: "I read that the club wanted to keep me - but when you want to keep someone, you do it by playing them. This hasn't been the case.
"I am very happy. I feel better already because I know I am going to play and string together matches."
Diarra added: "Portsmouth are a respectable club who are enjoying a good start to the season.
"There are talented players here - (Sol) Campbell, Kanu, Benjani (Mwaruwari), Muntari, (Glen) Johnson, (David) James."
Harry Redknapp certainly believes he has pulled off something of a coup in landing the "fantastic", if temperamental, former Le Havre player who will be officially unveiled at a press conference today.
The Pompey boss declared: "In my opinion he's already one of the best midfield players in the Premier League and has the ability to be one of the best there is.
"He's strong, powerful, quick and can pass the ball. You don't play for France for the last nine or 10 games unless you're top quality.
"I'm delighted he has decided to sign for us rather than a host of other clubs. It's great news for Portsmouth Football Club."