Hammers manager Sam Allardyce confirmed on Friday afternoon that the Moroccan has completed his move across London - but not in time to figure in Saturday's FA Cup third round tie against Manchester United at Upton Park.
Allardyce told Sky Sports News: "We've signed him for the rest of the season. I think that'll be it in terms of strikers as we need to get Andy Carroll back (to fitness)."
Chamakh, 28, struggled to claim a regular place in the Gunners' first team after initially impressing following a free transfer from Bordeaux in 2010.
Source: PA
Source: PA