Heat oil in heavy large Dutch oven over medium heat.
Add onion and saute until translucent, about 5 minutes.
Add rice and chard and stir until chard begins to wilt, about 3 minutes.
Add wine and simmer until absorbed, stirring occasionally, about 2 minutes.
Add 4 1/2 cups hot broth.
Simmer until rice is just tender and risotto is creamy, stirring frequently and adding remaining 1/2 cup broth by 1/4 cupfuls if mixture is dry, about 20 minutes.
Mix in 1/2 cup Parmesan cheese; season to taste with salt and pepper.