Trinder, who first worked at the firm in 2009 while at college, has rejoined and invested to become a partner alongside Philip Taubenheim.
Taubenheim and Trinder now own 50% of the business each and are joint partners.
The Gloucestershire auction house, which has a team of 12, had been owned by Taubenheim since 1992.
Taubenheim, 66, said: “Succession is always difficult in this industry… There’s a few years left in me yet, though Joseph will take the business on to even greater things.
“From the moment I met Joseph aged just 16, I knew there was something special about him. When he left, I thought I had lost him.
“Happily, instead, it has been rather like sending a son out into the world to learn from broader experiences before welcoming him back to the family business.
“I believe that in a year’s time the business will be much the better for it. It is a comfortable fit for a local lad and I am very excited to see his progression from here.”
Trinder, who is originally from Cirencester, said: “Philip has such a good name locally – what a great thing for me to be able to build on at the age of 30. It’s a gift.”
Since leaving Wotton in 2016 Trinder has worked at Dawsons in Berkshire, Halls of Shrewsbury and Gorringe’s in East Sussex.
Wotton Auction Rooms, which has traded in Wotton-under-Edge since the 1850s, will maintain its monthly general sales and, under Trinder, will develop a calendar of specialist sales for the future.