Katherine will join the cast as Detective Inspector Karen Renton who is tasked with finding who murdered Ioan Gruffudd’s character, Andrew Earlham, at the end of the first series.
Liar followed Laura Nielson, played by Joanne Froggatt, as she tried to prove that a psychopathic surgeon was a serial rapist.
Series two begins three weeks after the events of the first series as Katherine’s character attempts to uncover Earlham’s past and piece together the events leading to his murder.
Liar writers, brothers Harry and Jack Williams, said: “It has been a joy returning to Liar and our reunion with Joanne and Ioan. Equally we are thrilled to have Katherine Kelly on board as DI Renton after her stellar performance in Cheat.”
Liar will return to ITV next month.