Chamakh, 28, struggled to claim a regular place in the Gunners' first team after initially impressing following a free transfer from Bordeaux in 2010.
Chamakh hopes a spell at West Ham can kickstart his career following a frustrating spell on the fringes of the Arsenal team.
Speaking to the club's official website,whufc.com, the Morocco forward said: "I want to play and give my best for this team. I can bring my heading, some goals and we will see what else.
"I didn't have opportunities to play recently, but I did well before and I know I am a very good striker.
"We played only one striker at Arsenal, so I didn't play a lot, so I hope to do so more with West Ham."
"I think this will be a very important move for me and I don't want to waste any more time. I want to contribute immediately."