The 58-minute victory marks the fourth mixed title for the 41-year-old Nestor and second for his team in the last three grand slams.
He and Mladenovic won the Wimbledon title last summer after finishing runner-up at the French Open eight months ago.
"We've been playing our best tennis here," said Nestor. "It's great to win this title.
"I have what I believe is the best partner in mixed. Kristina helps me out and I have to cover less of the court — that's good at my age."
Nestor now owns three Melbourne mixed titles, winning with Elena Likhovtseva in 2007 and repeating three years ago with Slovenian Katarina Srebotnik. Nestor and Mladenovic beat Mirza and Tecau at Wimbledon last summer on the way to their title together.
Nestor's team beat the sixth seeds with five aces 14 winners, 24 unforced errors and four breaks of serve.
They broke Tecau on the Nestor passing shot to claim the first set in 28 minutes and broke Mirza twice in the second set with a Mladenovic passing shot past Tecau and sealing the victory.
"We learned from the loss we had the (U.S. Open) semifinals we were maybe a little bit too safe, especially me," said Nestor. "Since then we've been aggressive. "Any time you win, sometimes you get a little bit lucky, but our last few matches have been pretty convincing. I think the first round was probably our toughest match.
"The way we've been playing, there isn't that much to change. Especially this tournament, we've been in control most of the matches, so... Not that much needed to be done."
Nestor was accompanied on his trip by his family, which had to return home this week for school.
The Canadian will travel to Tokyo for next week's Davis Cup tie with Japan.