Mr Nixon has overseen operations at the North Yorkshire stately home for the past six years, as well as helping to manage its portfolio of businesses including a holiday park, retail, catering, farming and forestry.
He said: “I am delighted to be joining this outstanding organisation which does so much invaluable work for the agricultural industry.
“There is a lot of good work to continue and there are many opportunities for the Society to develop still further.
Speaking ahead of his retirement after over 20 years’ service to the charity, Nigel Pulling said: “I have thoroughly enjoyed my time at YAS, it is a fantastic organisation but having successfully negotiated the pandemic it is now the right time for someone else to take over.
“There is a great team of staff and volunteers in place, and I am sure Allister will lead YAS to further success.”
Mr Nixon, who is a chartered accountant and previously worked at Kantar Media, will be in post by the time of this year’s Great Yorkshire Show, set to take place in Harrogate in July.
Following a trial last year sparked by coronavirus restrictions, the show will become a permanent four day event.
YAS was formed in 1837, the same year as the first Great Yorkshire Show.
The charity became the first to buy a permanent showground in 1950 in Harrogate, where the show has been held ever since.