Mr Cranfield, already a director of Integrafin, will be Integrafin’s fourth chairman in two years when he takes on the role from 1 October.
He is expected to continue to be a partner in City law firm Allen and Overy LLP.
He takes over the chair from Christopher Munro who been interim chairman since August 2018. Mr Munro will remain as a non-executive director.
Patrick Snowball was appointed non-executive chairman in 2017 as the firm prepared for a stock market listing in 2018. He took over from then chairman and founder Mike Howard who stood down to become an executive director. Mr Snowball was then replaced by Mr Munro.
Transact floated in 2018 and is one of the leading platforms in the Financial Planning sector.
In its profit figures for the first half, ending 31 March, Integrafin reported it had increased funds over the same period last year from £29.7bn to £334.4bn, an increase of 8.7% over the period.
Pre-tax profits rose 19.8%, from £18.7m to £22.4m and net inflows for the first half of the year stood at £1.81bn. The firm revealed it has 173,000 clients.