He then studied chemical engineering at Iowa State University, obtaining his undergraduate, master's, and Doctor of Philosophy degrees from that institution.

[4][8] During his tenure at OSU, Halligan emphasized increasing retention and graduation rates,[8] halting a 12-year trend of decreasing student enrollments.

[10] They were credited with steering the university through the aftermath of the plane crash in January 2001 that killed ten members of the Oklahoma State Cowboys basketball team and their flight crew.

[5] He served two terms in that capacity and was a member of various committees, including appropriations, education, energy, business and commerce, finance, and rules.

[12][15] On August 12, 2015, Halligan released a statement through the Oklahoma State Senate announcing that he would not seek reelection to a third term and that the 2016 legislative session would be his last.