The playmaker moved to Hendon from Wasps in 2016 and has become an integral part of the squad, with his form earning him a couple of caps during the Red Rose's summer tour of Argentina.
However, Lozowski's status of playing second fiddle to Owen Farrell for both club and country has seen him linked with a switch away in search of regular rugby.
The 24-year-old, whose father Rob also played for England, has instead joined the likes of Farrell, Jamie George and Nick Isiekwe in signing fresh terms, much to the delight of boss Mark McCall.
"We are delighted that Alex has agreed a new deal," McCall said. "Alex will have an important role to play for us as he continues to develop as a player, so naturally we are very happy to announce that he will be staying at Allianz Park until at least 2020.
"In his brief time at the club, Alex has already shown how good a player he is, but the most exciting thing for us is how much improvement we believe there is to come from him alongside our core of young, hungry, home-grown players."