Garrison took over as fire chief in September of 2010. In a letter of resignation to Mayor Annise Parker, Garrison cited family concerns for his decision to step down.
His wife and infant grandson are still in the Phoenix area and Garrison says he needs to be closer to them as his grandson undergoes treatment for medical issues.
Mayor Parker says during his tenure, Garrison created a multi-year strategic plan for the department and also provided her with quarterly management and financial plans.
It was also on Garrison's watch that the department had its worst day. Four firefighters were killed when a wall collapsed during a motel fire in southwest Houston in May.
In his letter, Garrison says the deaths have had an impact on the whole department.
Mayor Parker says she's intends to find another chief who will continue many of Garrison's initiatives.