Lonergan was drafted in by Jürgen Klopp as Liverpool were short on goalkeeping options on their US tour in the 2019/20 pre-season. Lonergan continued to train at Melwood with the first team and after Alisson's injury in the first Premier League game of the campaign 35-year-old Lonergan signed a short-term contract with the Reds.

Lonergan's prime years were spent at Preston North End in the Championship from 2004-2011 and he was voted Preston's player of the year award in both the 2008/09 and 2009/10 seasons. Lonergan last featured regularly in the league for Fulham in the 2015/16 season, making 29 appearances in the Championship.

Although he never played a game for Liverpool, Lonergan picked up winning medals in the European Super Cup and World Club Championship as he was on the bench in both games. He was sub keeper for two Premier League games as well as the Champions League round of sixteen home leg with Atletico Madrid.

After leaving Liverpool in the summer of 2020 he agreed a short term deal with Stoke City in December that year. He played one League Cup game against Tottenham and then on 9th January 2021 joined Premier League West Bromwich Albion as a back up keeper, failing to make any appearances. On 20th August 2021 former Reds manager Rafa Benitez, now in charge at Everton, confirmed he had signed Lonergan on a season long deal to provide cover for Jordan Pickford and Asmir Begovic. He ended up staying for three years although never made an appearance for the club, being limited to bench duty. In July 2024, aged 40, he agreed a deal to join Wigan as player-coach. He was on the bench four times in League One games and retired from playing at the end of the season. In August 2025 he rejoined Liverpool FC as goalkeeping coach of the women's team.