Dillon issued a statement on his resignation Friday afternoon, citing issues related to his recent divorce and media attention because of it.
"It is with mixed emotions that I announce I have tendered my resignation to Governor Snyder. It has become clear to me -- as it likely is to most -- that it is unfair to my family and the residents of Michigan, to allow issues related to my recent divorce and the unfortunate acrimony associated with it to be a continued source of media attention and scrutiny," Dillon's resignation letter reads.
This move to step down comes a day after Dillon was questioned in a deposition for more than three hours in Lansing by lawyers for union workers and retirees opposing Detroit's bankruptcy filing.
The union claims state-appointed Detroit Emergency Manager Kevyn Orr has negotiated in bad faith while trying to restructure $18 billion or more in debt.
Dillon and Gov. Rick Snyder, who were involved in Orr's hiring, both testified this week.
Dillon was elected to the Michigan House in 2004, then re-elected in 2006 and was chosen to be speaker of the House. He was re-elected again in 2008.
Snyder appointed Dillon state treasurer in 2011.
"It is with regret but understanding that I accept Andy’s resignation," Snyder said in a statement released Friday. "He has been instrumental in many of the comprehensive reforms that are contributing to Michigan’s comeback. Andy has worked tirelessly on behalf of the people of Michigan, and we’re a stronger state because of his dedication, expertise and leadership."