In 1966, at the urging of Governor Romney, Brennan, sought the nomination of the Republican Party as Associate Justice of the Michigan Supreme Court. Brennan won the nomination, and the election. In 1969 and 1970, Brennan served as Chief Justice, the youngest Justice to serve in that capacity.
Founding the Thomas M. Cooley Law School
During his service on the Bench, Brennan received many requests for law school recommendations. This was the basis of his vision for a new, private, law school in Lansing, Michigan. In 1972, he incorporated the Thomas M. Cooley Law School. Brennan left the Supreme Court on December 6, 1973, to dedicate his professional career to the newly formed law school. Brennan served as first Dean of Cooley Law School until 1978, when he became its first president.
Judging the Law Schools is a law school ranking using only American Bar Association data, first published in 1996. The rankings, also known as the Brennan rankings, are compiled and published by Brennan. They measure objective American Bar Association statistics such as first time bar passage rates, course offerings, LSAT scores, tuition cost, academic facilities, employment, applicants, student and faculty diversity, as well as twenty other objective measures used by the ABA. Judging the Law Schools does not poll perceived reputation as do commercial publications such as U.S. News rankings, and no one statistic is weighted more than 3% in Cooley's ranking system. Because large schools tend to be ranked higher in Judging the Law Schools due to wider course offerings, greater numbers of applicants, and larger academic facilities, critics have alleged that the rankings favor larger institutions such as Cooley. Cooley relies heavily on its library statistics in its own "Judging the Law School" rankings. Specifically, Cooley has 10 library-based statistics in its 2010 rankings, which included separate entries for the total square footage in the library, the seats available in the library, the number of hours the library is open, the total number of volumes in the library, the total number of titles in the library, the number of librarians, the total hours that staff works in the library, and several other library-based criteria. Cooley has been subject to intense criticism and backlash for assigning equal value of these library-based statistics to far more important factors such as bar passage rate and percentage of graduates employed following graduation.
Death
He died in Lansing, Michigan on September 29, 2018.