Armstrong's departure has been announced shortly after Pentathlon GB courted controversy by appearing to endorse the International Modern Pentathlon Union (UIPM) move to replace the equestrian discipline with racing over an obstacle course.

Pentathlon GB has since insisted it does not support the contentious decision to axe riding, but wants to prioritise modern pentathlon preserving its Olympic status, so "will look to support UIPM in achieving this objective".

Armstrong told the Board of Pentathlon GB that he did not want to hold both positions at the same time, so will depart once a successor has been found.

A recruitment process is now underway to find his replacement.

One of Armstrong's last actions in the position was recruiting new performance director Jon Pett after the retirement of Jan Bartu, who led Britain to two gold medals at the Tokyo 2020 Olympic Games and numerous other medals since 2000.

Joe Choong won the men's event and Kate French claimed women's gold in modern pentathlon last year at Tokyo 2020.

Armstrong also oversaw the appointment of Trafford Wilson as the new Pentathlon GB chief executive last month.

"It has been a privilege to serve as chairman of Pentathlon GB since 2018," said Armstrong. 

"There hasn't been a dull moment from the hosting of the 2019 European Championships, the struggles through COVID, the incredible highs of Kate's and Joe's gold medals in Tokyo and more recently supporting our sport as it looks to define its future and to safeguard its Olympic status.

"I would like to thank all the athletes and staff for their tremendous hard work and contribution - it was fantastic to see yet another medal haul this weekend.

"I would especially like to thank my Board for their huge support and commitment, through some challenging times as well as some incredible highs."