Commissioned as a second lieutenant, he served six and a half years of active duty in the United States Army, including as a tank commander in the first Gulf War in Iraq, ending his service as a captain.

[3][4] He graduated magna cum laude and was awarded the Order of the Coif from the Sandra Day O'Connor College of Law at Arizona State University in 2001.

[citation needed] During Montgomery's tenure, the county attorney's office gained national recognition for its Restitution Specialist and Sex Assault Backlog programs.

[7] In August 2019, attorneys for Jodi Arias filed an ethics complaint against Montgomery, claiming he covered up misconduct and harassment by the lead prosecutor on the case.

[16] The commission did not pass Montgomery's name to the governor, which is required for a judicial apportionment, citing "concerns over the pattern of misconduct at the Maricopa County Attorney's Office and a lack of relevant professional experience.