The three schools are joining the "Catholic 7" defectors from the old Big East -- DePaul, Georgetown, Marquette, Providence, Seton Hall, St. John's and Villanova -- to create a new basketball-oriented conference with the same name.
The new conference, which like the old Big East will play its post-season tournament at Madison Square Garden, also announced a 12-year television partnership with Fox Sports Wednesday.
Butler and Xavier are coming from the Atlantic 10 Conference, while Creighton joins from the Missouri Valley Conference.
The move will become effective July 1.
"Joining the Big East is an unprecedented opportunity for Butler and represents an ideal fit for us -- academically, athletically, and geographically," Butler President James Danko said in a statement.