Evra, 36, arrived at the club’s Rush Green training complex on Wednesday morning before passing a medical and signing a short-term contract until the end of June 2018.
Sky Sports News understands Everton were also interested in the former Manchester United, Juventus and Monaco left-back but the player favoured a move to London.
Evra has been assigned the no. 27 shirt and could make his debut against Watford on February 10 at London Stadium.
He told West Ham’s official website: “I’m really happy to be a Hammer, to be back in the Premier League and I love this game!”
“It’s amazing to be back and I am thankful to West Ham for giving me the opportunity to do my job. When I wake up and know I am going to work hard, to have fun with my team-mates and give my best on the pitch, I want to say a massive thanks to West Ham, to the chairman, to the manager to all my teammates, who have given me a nice welcome, my agent and my brother.
“I’m just happy to be here, it’s really simple. You don’t realise how lucky you are and just to wake up this morning and know I am going to train with my new teammates made me smile!”
Evra, who spent eight-and-a-half years at United in total – including the 2013/14 season alongside current West Ham manager David Moyes – was sacked by Marseille earlier this season and banned by UEFA following an altercation with a supporter.
The ban, which runs until June 30, only relates to UEFA tournaments and does not prevent Evra from playing in any domestic competitions, including the Premier League.
Evra says he jumped at the chance to sign for West Ham once he was made aware of the opportunity to be reunited with Moyes.
He said: “It happened really fast. My agent called me and told me I needed to come back [from Dubai] to London as quick as I could and I had a nice meeting with the manager, who I know from Manchester United, of course, and I met the Chairman, so it was really easy.
“When you have to make a deal and money is not the issue, the deal could be done in five minutes. The main thing was for me to join West Ham and to help my teammates to win as many games as we can.
“It was the fastest thing I have done in my life, because both parties wanted to work together, so it was very easy to make an agreement.”