Singh, 38, proposed to girlfriend Gurkiran Kaur, 27, at a private party Tuesday night just blocks away from the Ontario legislature in Toronto where he served as a provincial legislator for six years.
Singh surprised Kaur, an entrepreneur and fashion designer, with the proposal in front of several dozen friends and family members at a vegetarian restaurant where they had their first date.
Singh was elected federal NDP leader last fall and had been guarded about his personal life, but social media posts in December made headlines after it was reported he and Kaur were engaged.
The couple shot down the rumours, saying it was instead a "rokha'' — a traditional Punjabi ceremony held ahead of a wedding and usually attended by close family.
Until December, Singh had declined to confirm or deny that he was in a relationship.
Along with friends and family, Singh invited several members of the media, including The Canadian Press, to witness the surprise proposal Tuesday night.
Friends cheered as Singh and Kaur arrived. Singh pulled a ring out of his jacket pocket and got down on one knee to propose to Kaur, who accepted.
A few moments later, the couple waded into the crowd and Kaur shouted, raising one hand in the air, "Every one, I'm engaged!"
Asked why he decided to make this news public and what he wants Canadians to know about it, Singh said he was excited about the engagement.
"I'm super excited to take this step forward — to have a life and future together with my partner," he said.