Evra, 36, joined David Moyes' side on a free transfer on Wednesday evening after three months without a club since his release from Ligue 1 side Marseille.
With the experience of 81 caps for France, five major international tournaments, seven league titles and a UEFA Champions League medal, the former Manchester United and Juventus left-back offers the Hammers a wealth of experience.
"The Patrice Evra of Man United is done. Now is a new challenge, which is the Patrice Evra playing for West Ham," he told the club's official website.
"I am proud and I'd like to say thanks to the fans, but the easiest part is to say it on camera, while the hard part is to give 100 percent of myself, every time I wear the shirt here, because I respect the people who got me here and it’s very important for me to give my best to the Club.
"People ask 'Why are you still playing? You have nothing to prove' but every day you wake up, you have something to prove to yourself. That's me."