The deal will see the Austrian international at the London club until the end of the current season with the option to make the transfer permanent.
"We have quantity as well as quality in central defence," Wolfsburg's sporting director Klaus Allofs said. "Emanuel hadn't been part of the first team recently. At West Ham United, he wants to win a place in the starting eleven."
The 52-time capped 30-year-old appeared in only eight matches since joining the Wolves in the summer of 2012 from Lower Saxony rivals Hannover 96. He now embarks on his second spell in English football, after having previously represented Middlesbrough FC between 2005 and 2010.