Grand-Am Road Racing, which runs the Rolex 24 race at Daytona Beach, is owned by NASCAR Holdings and has bought the American Le Mans Series.
"This announcement will transform sports car racing on this continent along with having world-wide industry implications," said Grand-Am president and CEO Ed Bennett at a news conference at Daytona International Speedway.
"Aside from the organisations involved, everybody wins - drivers, teams, manufacturers, sponsors, tracks and most of all the fans," he added.
The move further cements NASCAR's dominant position in North American motorsports business.
The two bodies will continue to run separate schedules in 2013 but a year later will begin a joint competition although a name has yet to be decided and the competitive class structure and rules have yet to be settled on.
The ALMS began in 1999 with Grand-Am starting a year later, both attempting to fill the gap left by the end of the IMSA GT Championship which had operated from 1971 to 1998.