Costello was appointed to the position of acting Klamath County District Attorney by Governor Kate Brown in 2017 after now-former District Attorney Rob Patridge. Following the appointment, Costello formally ran for office and won. She was sworn in on January 24, 2019.
On September 16, 2022, Governor Brown announced Eve Costello will resign, effective October 21, 2022.
Brown reportedly intends to fill the vacancy by appointment as provided in the Oregon Constitution.