The Reds have moved swiftly following injury to Alisson in Friday night’s 4-1 win over Norwich, which had left Klopp with few options between the sticks.
The 35-year-old—who spent much of pre-season with Liverpool, even playing 45 minutes against Sevilla in Boston—has now agreed a short-term contract.
Lonergan is likely to take a place on the substitutes’ bench against Chelsea in Istanbul, and provide experienced cover throughout the campaign.
Speaking to the club’s official website on Monday, Klopp praised Lonergan as a “brilliant character,” though he added Kelleher would take over as No. 2 on his comeback.
“He was in with us, he’s a brilliant character, a really nice lad and helped us a lot in the pre-season and now we decided to work together with him,” the manager said.
“So that’s a very experienced solution but in the moment when Caoimhin is back then obviously Adrian is No. 1, Caoimhin probably No. 2.
“But we have to see how then he can have some games with the under-23s or under-21s [so] that he gets match practice as well.
“We have to see how that works but that’s then how we cover that situation.”
Undoubtedly the biggest side on the veteran stopper’s CV, Lonergan has also played for the likes of Preston, Leeds, Bolton and Wolves, along with representing both England and the Republic of Ireland at youth level.
He was last on the books at Middlesbrough, but failed to make a single outing for the Championship club and spent a short period of last season on loan with Rochdale.
This is considered an emergency signing for the Reds, and it is highly unlikely Lonergan will play for the first team this campaign.
Lonergan follows in the footsteps of Alex Manninger, who was signed to provide experienced cover ahead of Klopp’s first full season with Liverpool in 2016.