The stadium opened in August 1971 as Schaefer Stadium, primarily as the home venue for the renamed New England Patriots of the National Football League. The team was known as the Boston Patriots for its first eleven seasons 1960–70, and had played in various stadiums in the Boston area. For six seasons, 1963–68, the Patriots played in Fenway Park, home of baseball's Boston Red Sox. Like most baseball stadiums, Fenway was poorly suited as a football venue. Its seating capacity was inadequate—only about 40,000 for football—and many seats had obstructed views. With the completion of the AFL–NFL merger in 1970, the league required its teams to play in stadiums which seated more than 50,000, and no venue in Boston proper could accommodate a crowd this size with NFL amenities. Indeed, before the Patriots arrived, numerous previous attempts at pro football in Boston had been stymied by the lack of a pro-caliber stadium. (The Redskins left after the 1936 season, in which they hosted the NFL Championship Game, not in Boston but at the Polo Grounds in New York City.)
The Boston Patriots played the 1969 season at Alumni Stadium at Boston College in Chestnut Hill, and the 1970 season, their first in the NFL, at Harvard Stadium in Boston's Allston neighborhood.
The site was selected when the owners of Bay State Raceway donated the land, midway between Boston and Providence, Rhode Island. The general contractor who built the stadium was a Massachusetts-based company named J.F White Contracting Co.
Ground was broken in September 1970, and it cost $7.1 million, only $200,000 over budget. Even allowing for this modest cost overrun, it was still a bargain price for a major sports stadium even by 1970s standards. This was because the Patriots received no funding from the Commonwealth of Massachusetts or the town of Foxborough; indeed, it was one of the few major league stadiums of that era that was entirely privately funded.