The pacey centre-back had been pursued over the summer to add depth to a defence that was without the injured Kolo Toure and Sebastian Coates at the weekend and relied on the inexperienced Andre Wisdom and Martin Kelly as cover for Daniel Agger and Martin Skrtel.
Ilori becomes Brendan Rodgers’ sixth signing of the summer transfer window and follows fellow defender Toure, left-back Aly Cissokho, goalkeeper Simon Mignolet, and attackers Iago Aspas and Luis Alberto.
|6/1||Liverpool are 6/1 with BetVictor to sign Leandro Damiao
"I'm going to try and achieve everything I can. I want to play as much as possible and we'll see what the future holds. I will give my all and try my best to help the team.
"I know the history of the club and the Premier League is the best league in the world, in my opinion. Liverpool have a great team and I think it's the place for me to be at the moment.
"I know there have been some great teams here in the past and the club has won a lot of trophies and I want to be a part of it."
The 20-year-old was born in London but has represented Portugal at U18, U19 and U20 level and made 11 league appearances for the Lions last season.
Liverpool are also expected to complete a move for Paris Saint-Germain defender Mamadou Sakho and a loan deal for Chelsea winger Victor Moses by the close of the transfer window on Monday evening.