Seth Stepien, 19, waived his right to a trial by making the plea. In exchange for the plea, he will not face a felony firearm charge.
Stepien will be sentenced May 22.
Officials also agreed that his minimum prison sentence is not to exceed nine years and that it will run concurrent with the sentence being served from his conviction in Kent County.
The Ottawa County charges evolved from an incident that occurred during the Coast Guard Festival in Grand Haven. The crime happened in the parking lot of the Tri-Cities Family YMCA at about 10:35 p.m. Aug. 5, 2016.
Two 17-year-old Montague men reported that they were robbed at gunpoint, according to Grand Haven Public Safety Director Jeff Hawke. Cellphones and jewelry were taken.
In Kent County, police said that Stepien and Austin Luft, 20, of Lowell used social media to arrange a hold-up at a Kent County park, allegedly targeting a woman who was looking for prescription medication. When the woman arrived to complete the deal, she was robbed at gunpoint.