The access points are being supplied by US firm Wayport, which will receive an undisclosed sum from Nintendo.
"This agreement with Wayport will bring countless people together to play games in a single, simultaneous wireless community," said Reggie Fils-Aime, Nintendo of America's executive vice president of sales and marketing.
"Nintendo Wi-Fi Connection is simple to use. Beginning with free access at participating McDonald's, we have removed one of the major barriers that have kept people from going online to play games."
The first online games, Mario Kart DS and Tony Hawk's American SK8Land, are due to be released next month.
Two more games, Animal Crossing: Wild World and Metroid Prime Hunters, are due to be available by the end of the year.
In its statement, Nintendo said that its forthcoming next-generation game console, set for release in 2006, would also connect to the online gaming service.
