Zac Toumazi will step down from his position as Sussex chief executive at the end of 2016.
He took over the role from Dave Brooks in 2013, after previously working at both Surrey and Hampshire.
"It has been a difficult decision to make but I do believe that it is right for me to move on and hand over the reins to a successor," Toumazi said.
The Division Two side began their final County Championship match of the season against Gloucestershire on Tuesday.
BBC Sussex's Adrian Harms: "This has been a difficult season for Zac Toumazi particularly as performances on the field, notably in white-ball cricket, haven't matched the expectations of the Sussex supporters.
"However, it has also been a traumatic period for the club off the field following the tragic death of young bowler Matthew Hobden, and Toumazi deserves great credit for the way in which both he and the club responded to the tragedy with great dignity.
"He leaves at a time of great change in county cricket, particularly with a new T20 competition seemingly inevitable, and the members will expect a prompt appointment to steer Sussex through what are likely to be choppy waters ahead."