The former Chelsea midfielder has signed for The Cottagers on a two year deal.
"Alexei's quality speaks for itself and we had to beat off some fierce competition from other Premiership clubs to get his signature, so it's a feather in our cap that he's chosen to come here," manager Chris Coleman told the club's official website.
"He is another versatile player, he can play centre midfield, centre-back and he reads the game so well with great experience, so I'm delighted that he has joined us.
"All in all I think we have had a very successful transfer period and I'm looking forward to pushing on now and climbing the table, and I've no doubt the new additions will help us do that."