Professional trustee appointments grew by 8% over the past year, slowing from 11% growth the previous year, according to a survey from WTW.
The total number of appointments reached 2,711 across the industry.
Growth is expected to slow further to around 5% over the next three years as the market matures and more pension schemes move towards buyout and wind up due to improved funding.
Sole trustee appointments also rose by 8%, compared to 14% the year before, with future growth estimates at about 6% over the next three years.
Sole trustees now make up about half of all professional trustee appointments, mainly for small schemes, where they account for nearly 70% of appointments to schemes with assets under £25m.
For large schemes with assets over £1bn, 94% of appointments go to a trustee board, either as trustee chair or co-trustee.
Mustafa Bharmal, professional trustee group director at WTW, said: “The Professional Trustee market is still growing at a very healthy rate.
“Following a flurry of PT appointments over the past few years, rates of growth have started to stabilise as around half of all defined benefit pension schemes now have a Professional Trustee in place.”
Nausicaa Delfas, CEO at the Pensions Regulator, said: “We welcome the valuable insight and perspectives provided by this and other surveys in a fast-changing pensions market.
“Professional trusteeship has experienced huge growth over the last few years, bringing new risks and opportunities.
“We expect all new appointments to have followed a robust process, and to protect savers we have extended our market oversight approach to the 11 largest firms.”