The former Olympic champion will become the first woman to wear a green beret when she is officially appointed to her part-time role in the New Year.
The super-fit cyclist, who has won gold twice and was made a CBE by the late Queen, has been recruited to inspire young women to consider the Marines as a career choice.
In 2015 she switched from cycling to horse racing – and won her first event as a jockey the following year.
Last week the 43-year-old joined rookie commandos on a forced march across Dartmoor, where she completed the 30-mile endurance test and then presented the successful recruits with their coveted green berets.
The decision to appoint her comes as the elite corps finds itself the only infantry force in the UK yet to recruit a woman to its ranks.
At least five have passed the Army’s six-week ‘All Arms Commando’ course as opposed to the 36-week Royal Marine test.
More than 20 female applications have been made to the Navy to join the 359-year-old corps. Of those, only two started the course at the Commando Training Centre in Lympstone and, despite being very good, both failed.
All Royal Marine recruits must pass the physically demanding nine-month Commando course, regarded by many as the most testing infantry selection of any unit within Nato.
The soon-to-be Colonel Pendleton will take up her duties alongside two other ambassadors – Bear Grylls and Colonel Baron Sir Mark Sedwill, the former Cabinet Secretary who sits as a crossbencher in the House of Lords.
He is also the President of the Special Forces Club.
In her new role, Victoria will attend events for both officers and marines as they mark their 360th anniversary next year.
Her partner Louis Tinsley is a former Special Forces soldier and several years ago she took part in the TV series Who Dares Wins.
A Royal Marines source said: “Victoria has experienced hardship through her training and has represented Great Britain at the highest level of sport.
“She is an inspiration to young men and women.”
Victoria will not be the first woman to serve in the Royal Marines. In 1747 Hannah Snell took on the persona of James Gray, wore men’s clothing and joined the Marines, serving on warship HMS Swallow.
