The donation was to be formally announced Monday.
The campus is already home to the Lee and Joe Jamail Texas Swimming Center, Joe Jamail Field and the football stadium, the Joseph D. Jamail Pavilion and the Joseph D. Jamail Center for Legal Research.
UT President Bill Powers Jr. said $10 million of the latest donation will go to the law school, with the rest split between undergraduate programs and the nursing school.
The law school and nursing school will use the money to recruit and retain faculty. The nursing school also will create a fellowship for students seeking doctoral degrees. About $2.5 million will endow and support a freshman advising center, Powers said.
Jamail is best known for his 1985 $11 billion victory for Pennzoil over Texaco, but his interests have always varied. He supported the first of Willie Nelson's annual picnics in 1973 with a $5,000 loan.
UT declined to say how much money Jamail has given to the school over the years, citing his request that they not. Jamail himself pegged the total at "millions and millions."
"I'm just doing what any decent guy with enough money to do it should do," he said. "Whether it's $50 or $50 million, it doesn't matter."