The Nigeria international forward passed a medical at Melwood on Monday after Jose Mourinho decided he was surplus to requirements at Stamford Bridge.
Moses told the Anfield club's website: "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.
"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."
Moses began his career at Crystal Palace before spending two years with Wigan. He joined Chelsea in January 2012 and went on to make 42 appearances for the club, scoring 10 goals.
The 22-year-old is the third deal to be concluded by Liverpool in the last 24 hours following the earlier announcements of defenders Tiago Ilori and Mamadou Sakho.
Eight players have now been brought in by Reds boss Brendan Rodgers this summer, with Monday's arrivals following those of Kolo Toure, Iago Aspas, Luis Alberto, Simon Mignolet and Aly Cissokho.