Larry Timothy O'Neill, 56, said he "made a terrible mistake when I was 18 years old."
He was paroled last May after pleading guilty to second-degree murder for the shooting death of 31-year-old Derwood McComb in 1975.
"I was a kid. I am no longer a kid," he said. "I got a life, a 2-year-old son and own the house I live in."
The Democratic candidate shot McComb in the head with a rifle, then called police and confessed. O'Neill led investigators to where he dumped McComb in Summit Township; the man died later at an Ann Arbor hospital.
O'Neill was initially charged with first-degree murder and conspiracy to commit murder, but pleaded guilty to a lesser charge of second-degree murder.
He said boosting low-income housing is his priority and he'll ask voters for other ideas.
He faces fellow Democrats Adam Shelton and Daniel Mahoney in an August primary. Mahoney is the nephew of current Commissioner Gail Mahoney, who has served for 20 years but said she would not seek re-election.