The Ethiopian finished in a time of two hours 10 minutes 35 seconds, while Kenyan runners Kiplimo Kimutai and John Kiprotich followed close with times of 2:11:20 and 2:11:29, respectively.
"It was very cold and it was raining so I'm very happy to win," said Warga. "I didn't run my personal best it was a little windy but with this result I am happy."
New Zealand's Mary Davies, who lives in Ottawa, passed Kenya's Agnes Kiprop with just two kilometres left in the race to finish first in the women's race with a time of 2:28:56.
Kiprop was second (2:29:32) and Ethiopia's Radiya Adilo third (2:30:49) among the 25,000 runners participating.
"At about 39 kilometres I could see the girl and I thought maybe I could catch her. I didn't have much energy left," Davies said. "I felt strong at 40 kilometres when I passed her but kept looking around for her."
Matt Loiselle of Toronto was the top Canadian on the men's side, finishing in seventh overall with a time of 2:16:23. Krista Duchene of Brantford, Ont., was the top Canadian woman with a time at 2:32:15 to place fourth.
Duchene said she was troubled by her hip early on.
"With my hip giving me trouble at six kilometres, I thought at least I could go under 2:30, and then it was just hurting," she said.
Chilean runner Francisco Mendez placed first in the half-marathon category with a time of 1:07:48.
Organizers says $3.7 million was raised for 167 charities.