Keating's resignation was submitted only after he refused a directive from the university president to fire Blaney, who was hired three years ago after P.J. Carlesimo left to coach the Portland Trail Blazers.
Blaney had two years left on a contract that pays him about $300,000 annually.
The dismissal came just four days after Rutgers, New Jersey's other Big East school, fired coach Bob Wenzel after nine seasons.
Blaney, who coached the previous 22 seasons at Holy Cross, had a 38-48 record at Seton Hall, including a 19-35 Big East Conference mark.
Despite a major recruiting coup in landing freshman sensation Shaheen Holloway this season, the Pirates had their worst record under Blaney, going 10-18, including 5-13 in the league. as ousted in the first round by West Virginia.
Blaney felt he wasn't given enough time at Seton Hall, noting that there is a lack of patience and tolerance in college basketball.
"I really wanted to finish the job, so my emotion was disappointment," Blaney said of his firing in an interview with MSG Network.
Blaney did not discuss the reasons given for his firing, but held and emotional meeting with his players after the firing.
"We came in and he told us he was not good at giving end of the season speeches and that this was the first time in his life he had ever been fired from a job," the Pirates' Levell Sanders told MSG. "It was kind of tough. He broke down and everybody in there felt sorry for him. Some guys took it hard and were crying. He's a great person, he helped a lot of us."
Keating, who was the athletic director for 12 years, did not return a telephone message left at his home.
Monsignor Robert Sheeran, the university president, made it clear in a statement that he fired Blaney.
"After discussing this with Larry Keating, it became clear that we were not in agreement about how this will be accomplished," Sheeran said. "While a decision like this is difficult, I am confident that this is what is best for Seton Hall, our student-athletes and our future."