The latest figures, released by parent company IntegraFin Holdings, relate to the six months ending 31 March.
They showed net inflows of £2.2 billion, up from £1.7 billion in the same period in 2017.
Assets under administration reached £29.8bn, a £1.8 billion increase from the end of 2017.
The results were achieved in the teeth of what the firm called “significantly less favourable market conditions in the second quarter.”
Pre-tax profits also increased from £17.3m to £18.7m, when compared to the same period last year.
Ian Taylor, chief executive, said: “Following a successful IPO, we are pleased to announce a pleasing set of results for the first half of the year.
“Despite the backdrop of stock market volatility, Transact achieved its highest ever H1 inflows.
“Given our differentiated premium offering and the quality of the service we offer to advisers and their clients, we remain confident in our ability to sustain growth as we move into the second half of the year.”