Tisch died at his home, a family publicist said.
Three weeks ago on Oct. 25, the Giants' other co-owner, Wellington Mara, also died of cancer. Wellington Mara was the son of team founder Timothy J. Mara.
Mara was the son of team founder Timothy J. Mara. Tisch bought 50 percent of the Giants in 1991 from Tim Mara, Wellington Mara's nephew, not long after the Giants beat Buffalo in the Super Bowl.
"To lose Bob Tisch so soon after we lost our father is especially heartbreaking for the Mara family," said John Mara, the Giants' chief operating officer. "He not only was a great business partner, he was a dear friend to our family and to me personally. ... We will miss him terribly, and we will never forget everything he did for our family, our team and the numerous charitable causes to which he was devoted."
He also was U.S. postmaster general from 1986-88 and chairman and director of Loews Corp., a company he and his late brother, Laurence Tisch, had purchased in 1959 when it was a movie theater chain. The company changed its name from Loews Theaters in 1971 and currently owns and operates Loews Hotels, the Lorillard Tobacco Co. and Bulova Corp., among other interests.
Tisch was diagnosed with an inoperable brain tumor in 2004 and had curtailed his regular visits to Giants practices and games.
During his illness, his son, Steve Tisch, was named the Giants executive vice president and took on a larger role in the operations of the team, particularly in the negotiations between the Giants and the state of New Jersey over a new stadium at the Meadowlands sports complex.
The Giants will continue to be co-owned by the Tisch and Mara families.
Steve Tisch and brother Jonathan Tisch, the Giants' treasurer, addressed the team after practice on Saturday, the day before the Giants lost to the Minnesota Vikings at the Meadowlands.
"I wanted to express to the players, the coaches and really the whole staff what being involved with the New York Giants has meant to my father," Steve Tisch said. "For the 14 years he's had the privilege of owning this team, it's been the greatest gift for him, professionally and personally."
A native of New York, Robert Tisch was involved in numerous civic organizations in the city. He served as the chairman of the New York Convention and Visitors Bureau for 19 years and was chairman of the Citizens Committee for the Democratic national conventions held in New York in 1976 and 1980.
Mayor David Dinkins in 1980 appointed Tisch the city's ambassador to Washington, a post he held through 1993. He also was chairman of the New York Chamber of Commerce and Industry from 1990 to 1993.
Football was his love, his family said.
"It gave him so much pleasure and so much pride," Steve Tisch said. "Sunday after Sunday after Sunday, this is what he lived and loved."
Among the charitable organizations Robert Tisch helped found was Take the Field, a nonprofit corporation that has raised more than $130 million to renovate and rebuild public school athletic facilities in New York.
Born Preston Robert Tisch on April 29, 1926, he attended Bucknell University and, after serving in the military in World War II, earned a bachelor's degree in economics from the University of Michigan.
He is survived by his wife, Joan Tisch, and three children.