He returned to India in July 1927 on orders from Bhagat Singh. He was accompanied by 25 associates from the U.S. and brought a consignment of revolvers and ammunition.
He came into the limelight for the assassination of General Michael O'Dwyer -the man responsible for Jallianwala Bagh massacre . Shaheed Udham Singh witnessed the Jallianwallah Bagh massacre and it was then, he took an oath to avenge the killings.
He fought many odds before he could reach his final goal of killing Michael O'Dwyer 21years after the massacre happened.
Mass killing in Jallianwala Bagh proved a turning point in his life. After a bath in the sacred sarovar at Golden Temple,Udham Singh took a silent vow and solemn pledge in front of the Golden Temple to wreak vengeance on the perpetrators of the crime and to restore honour to what he saw as a humiliated nation.