The Reds had already brought in defenders Tiago Ilori and Mamadou Sakho from Sporting Lisbon and Paris St Germain respectively.
Moses only joined Chelsea last summer, scoring 10 goals in 42 appearances, and his switch was confirmed on transfer deadline day after he passed a medical at the Anfield club.
Moses told Liverpoolfc.com: "First and foremost, I'm delighted to have made the loan from Chelsea to a big club like Liverpool.
"The most important thing is for me to be professional about it and I'm here to do a job for the club.
"The target is to get into the top four and for the club to compete in the Champions League - and I'm delighted to be here.
"The manager has done very well and the formation and players here will help me and I just want to gel in, get to know the players and play with them.
"There are a lot of quality players here - they're winning games and creating chances. It's a massive thing for me to be here."