The Merseyside club have offered the player a four-year-contract and Cahill is expected to complete the formalities within the next 24 hours.
The move comes after the player refused to join south London neighbours Crystal Palace two weeks ago and relations between Cahill and Lions chairman Theo Paphitis have soured in that time. The midfielder refuted Paphitis' claim that he had demanded a transfer twice while Cahill has always claimed that he was not looking for a move away from The Den.