Out of the 13 Lok Sabha seats, Congress could bag only three seats as against eight seats won by it in 2009.
"I wish to resign as the spokesperson of Punjab Pradesh Congress Committee, owning moral responsibility for the poor performance of the party in Punjab," Khaira said in a letter to party vice president Rahul Gandhi.
Khaira was appointed as spokesperson of Punjab Congress in April last year.
"I have discharged my duties honestly, fearlessly and relentlessly and left no stone unturned to oppose... the anti-people and unconstitutional policies of the SAD-BJP combine government," he wrote in his letter.
Khaira said he tried his best to strengthen the party in the state but somehow the Congress was unable to deliver or convert the strong anti-incumbency factor against the SAD-BJP government into votes.
"I take full moral responsibility for the poor showing on the hustings and offer my resignation from the post," he said.