BOSTON — Shawn Collins is resigning as executive director of the Cannabis Control Commission effective Dec. 4, Acting Chairwoman Ava Callender Concepcion announced Thursday, providing some clarity around one of the two leadership questions that has hung over the commission for months.

The upheaval at the CCC erupted into public view in July when Chairwoman Shannon O’Brien announced during a meeting that Collins would be taking parental leave and then leaving the commission by the end of the year. In September, Collins denied to the News Service that he had any firm plans to leave the agency and O’Brien was suspended from her position by Treasurer Deborah Goldberg based on “[s]everal serious allegations” that were made by an unnamed commissioner and CCC staff about O’Brien’s behavior.

“That would be something I’d want to talk about with the commission as a whole. Again, I think making sure there’s a plan in place for that succession is important. It’s something that commissioners have raised in public meetings throughout the last year,” Collins, the only executive director the CCC has had since it was formed in 2017, said in September about leaving the agency by the end of the year. “At this point, there is no concrete plan for the end of the year.”

It is unclear whether Collins discussed his resignation with the commission. He has been out of the CCC office on parental leave for about two months and was expected to remain on leave until early December. Last month, commissioners voted to make Chief People Officer Debra Hilton-Creek acting executive director.

As she opened Thursday’s meeting, Concepcion announced that the commission “received notice from Executive Director Shawn Collins that he will be resigning effective December 4” and read from a letter he sent.

“Serving as the commission’s inaugural executive director has easily been the most profound and rewarding professional opportunity of my life. No matter what my future holds, I’m confident that the ability to help create new government while ushering in the migration of cannabis legalization in the commonwealth cannot be matched by any other professional pursuits,” Collins wrote, according to Concepcion. “As a result, I’m eternally grateful to you, madam acting chair, all commissioners past and present, and most especially the immensely talented public servants that comprise the agency staff. I’ve learned something every day in this role and that privilege will never be lost on me.”

Collins was unanimously chosen in the fall of 2017 to lead the CCC as its inaugural executive director. Prior to that, he was an assistant treasurer who served as Goldberg’s point person on pot during the debate over legalization and until oversight of marijuana was removed from the treasurer’s direct auspices by the Legislature in a rewrite of the 2016 ballot law. He had previously worked as chief of staff and general counsel to Sen. Richard Moore and served as chairman of the Webster School Committee.

Concepcion said at Thursday’s meeting that the CCC plans to launch a search for a new executive director. But first, commissioners want to review the executive director’s job description, revisit a memo that delegates certain authority from the commission to the executive director, and more.

“We obviously want to start thinking about the process in the next few months. Because finding the next executive director of this agency is not going to be an easy task. And it’s a big, big job, and we need to make sure that we’re looking at all those factors,” Commissioner Nurys Camargo said.

During the hiring process that ended with the selection of Collins as executive director, the CCC held public interviews with its three finalists: Collins; Erin Bradley, then the executive director of the Children’s League of Massachusetts and now vice chair of the Milton Select Board; and Norman Birenbaum, who was then a principal analyst at the Rhode Island Department of Business Regulation and is now the U.S. Food and Drug Administration’s chief cannabis adviser.

Aside from the uncertainty around the executive director position, there is also the question of the position of CCC chair. O’Brien was tapped by Goldberg for that role last fall, but has been suspended with pay for two months. O’Brien sued Goldberg to be reinstated as CCC chair, but that lawsuit is on hold pending a meeting between the two women. That was originally supposed to take place Nov. 7, but was rescheduled to Dec. 5.

Concepcion has been leading most CCC meetings as acting chair since O’Brien was suspended. She was initially set to serve in the acting chair role until Nov. 9, when the process around the CCC’s new regulations was complete, but commissioners voted last week to extend that to Dec. 15, according to CommonWealth Beacon.