She takes over permanently from Dale Cobb, who resigned in October, with union stalwart JB Phillips coming back to act as interim chief executive until the appointment.
Belsham had planned to finish with the greyhound club today, but agreed to stay on for two more weeks as the search continues for her replacement, before heading to her new office beside Cooks Gardens after a short break.
She will become the third woman currently running a New Zealand provincial union, the largest compared to her contemporaries Susan Knight (King Country) and Cushla Tangaere-Manuel (East Coast).
Before his departure, Cobb said the role was demanding and required a diverse skill set, particularly given they must deal with many different viewpoints and personalities across a vast range of administrators, players, coaches and supporters.
But coming from the racing world, which is also male-dominated, Belsham said it won't be a problem.
"The industry I'm currently in, it's nothing I'm not aware of in my life.
"I know they have high expectations. I've got quite a bit of learning around the processes and procedures.
"I don't clock watch. I've done some really bizarre hours in this [greyhounds] job. I'm aware you will be seen as the face of Wanganui rugby."
Primary among her immediate goals are fostering the youth grades in Wanganui, which took a hit in recent years with local secondary schools entering their teams in Manawatu competitions, while using her extensive business experience to ensure the balance sheets stay in proper order.
"It's important that our finances and cash flow are fine. That's one thing we need to secure."
Although she will not officially start for another month, Belsham has indicated to the WRFU she wants to be involved in the interview process for the new rugby development officer, which is the last piece of the puzzle for the new-look team.
In the elections at last year's annual meeting, Norm Crowe became the new WRFU president and Jeff Phillips the chairman, while after being introduced at the end of the season, Paul Kenny will now have his first full year as club development officer.
Phillips said the initial field of 16 candidates for the chief executive job was worked down to four contenders by a WRFU board member and an independent delegate sent from the New Zealand Rugby Union offices in Wellington.
"It just removed the bias, from everybody knowing everybody from Wanganui."
Phillips and another delegate then joined them to make up the final selection committee.
"Out of the applicants, there was a high calibre, she stood out more for the experience of the business side," he said.
"Not just money's tight, the Wanganui union is a business at the end of a day, and it needs to be run like a business.
"There's a whole lot of little things that need to be tidied up.
"She's got strengths in areas that maybe Dale didn't have, and she can develop in those areas where he was strong.
"She's going to have a big crash-course in a hurry."
Regarding making a progressive choice with a woman in charge, Phillips pointed to the success of New Zealander Raelene Castle, who took over the running of the Bulldogs in the NRL.
"She never played rugby league. You don't need to be a former player, so long as you understand the game."
Taranaki born, Belsham got into sports management when she spent 1994-97 with the Wellington Racing Club, including being events co-ordinator.
She met her husband and racehorse trainer Paul Belsham and they moved to Wanganui, where she spent three years with a local law firm before joining Westpac Bank, finishing as local business manager.
In 2012, she joined the greyhound club and was project manager for the new $1.5m grandstand at Spriggens Park, while also overseeing the club's multi-million dollar turnover.
Mother of two daughters, Belsham has also had financial responsibilities with the Kaitoke School Board of Trustees (2007-13) and as treasurer of Marie McFarland Kindergarten (2005-7).
