Kingsbury beat Ikuma Horishima of Japan, who started strong in the final head-to-head race but lost control and had to bail on the required second jump. Australia's Matt Graham took bronze on a sunny day in the mountain town of Livigno.
The gold handed Canada their first title of the Milano Cortina Games.
Kingsbury, at 33, the oldest man racing in dual moguls, has claimed a medal in each of the four Olympics he has competed in. He is widely regarded as one of the greatest moguls skiers of all time.
"I really wanted this one, and I knew it was my last Olympic performance," Kingsbury said. "I gave everything. I had no regrets."
On Sunday, he held both skis high in the air as he was proclaimed the winner. He closed his eyes and sang along to the national anthem as he stood on the podium. Fans in the crowd waved red-and-white Canadian maple leaf flags.
Kingsbury later held his 18-month-old son, Henrik, who wore a red knit cap with the words 'Go Mik'.
Dual moguls is a new event at the Olympics, pitting skiers together in a head-to-head elimination format in which two competitors race side-by-side through parallel bump fields. Speed counts, but so do turns and aerial manoeuvres.
Horishima, 28, won bronze in the single-format moguls.
Australia's Cooper Woods, who edged Kingsbury to earn gold in the men's singles, was eliminated in the dual moguls' second elimination round after missing a jump.
Woods, 25, said he had mixed emotions after his prior win.
"I wanted to come out here and perform to my best, and I didn't do that, which is really upsetting," Woods said of his dual moguls appearance.
On Saturday, Australian Jakara Anthony won gold in the women's dual moguls.