The 54-year-old revealed his decision to members and season ticket holders at Tuesday night's Annual General Meeting at the County Ground, with the club confirming the news on Wednesday.
A player and coach at the club since 1982, Ripley will not be leaving Northants though, as he is to stay on in an alternative coaching role away from the first team.
Ripley steps down from the head coach role having enjoyed a roller-coaster of a stint, and he is set to be replaced at the helm by current assistant coach John Sadler.
After taking over from his close friend, the late David Capel, midway through the 2012 season, he won two T20 Blast titles in 2013 and 2016 as well as finishing runners-up in 2015.
He also steered the club to two promotions from the County Championship division two in 2013 and 2019.
There have also been some lean years though, and the team has struggled for form and consistency over the past couple of seasons, with Ripley admitting the Steelbacks' poor performance in the 2021 Vitality Blast making his mind up that it was time for a change.
Despite targeting the competition as a priority, Northants never got going and finished bottom of the North Group, and that hit Ripley hard.
"I have been here before, in 2019 I was challenging myself as to whether I was still taking the group forward," Ripley told BBC Northampton.
"Obviously we then got promotion and we had some success, and then some new coaches arrived (John Sadler and Chris Liddle).
"That changed the dynamic a little bit and I fed off that, and we have obviously had the pandemic to get through.
"But when we finished bottom of the T20 league I think that was pretty much me done, and thinking it was time to hand it over to somebody else."
And he added: "I have had my time, I think that is just the bottom line.
"I am fortunate enough to have had some highs, that is why I have done nine years, because if you don't have the highs you don't get too long in the head coach's role.
"But there has been some tough times as well, and I think eventually it has caught up with me."