McKinnon received her undergraduate degree from Goucher College in 1982 and her J.D. from the University of Baltimore School of Law in 1986. She began her legal career as a law clerk for a Baltimore city circuit judge in 1986, and worked for the Baltimore City State Attorney’s Office from 1987 to 1991 and as an attorney in private practice from 1991 to 1995. McKinnon served as deputy Glacier County attorney from 1996 to 1997 and as deputy Teton County attorney from 2001 to 2006. She was a judge on Montana's 9th District Court from 2007 until being elected to the Montana Supreme Court in 2012. McKinnon is a member of the District Court Performance Measurement Advisory Committee to the Montana Supreme Court and the Judicial Education Committee.
