Sakho was at Anfield to watch the Reds' 1-0 win over Manchester United on Sunday, along with fellow new-boy Tiago Ilori and Victor Moses, who is expected to complete a season-long loan move from Chelsea.
| LIVERPOOL LATEST
|6/1||Liverpool are 6/1 with BetVictor to sign Tom Ince
"I'm delighted to be here. I'd like to thank everyone for the welcome," Sakho told the club's official website.
"I came here because the project that is in place at Liverpool interests me. I'm really looking forward to playing my first game."
Sakho becomes Brendan Rodgers' seventh signing of a busy summer, joining Simon Mignolet, Kolo Toure, Aly Cissokho, Luis Alberto, Iago Aspas and Ilori at Anfield.