Secrest has worked in the attorney general's office since 2001. He became chief deputy in 2010.
In his new role, Secrest will continue to develop litigation strategy and serve as the office's representative on various boards and commissions.
Among other duties, Light as chief deputy will act as the attorney general's liaison with the Indiana General Assembly.
Light was involved in designing the settlement package for victims of the 2011 Indiana State Fair stage collapse.
Attorney General Greg Zoeller announced the moves Thursday.