The 29-year-old will turn 30 tomorrow and signs on a two-and-a-half-year deal.
Lauren told the official Pompey website: "This is a great move for me. Portsmouth are having a great season and are pushing for a place in Europe and I aim to be playing my part in that challenge. I have been very impressed with the club's plans for the future both on and off the pitch and this was why I chose to come to Fratton Park. It will also be good to once again team up with Sol Campbell and Kanu."
I think this is a great signing for the club. Lauren may be a bit on the dirty side at times but it's great to have the option of a strong, imposing right back who can get forward. Will he play in the same team as Glen Johnson? We shall see.
Now we have half of Arsenal's famous unbeaten defence of the 03/04 season. Now we just need to sign Toure and Ashley Cole!
Welcome to Pompey Lauren!