Impax Asset Management has seen its assets rise by 84 per cent to £37.2bn over the past year.
In the 12 months to the end of September 2020, Impax saw record net inflows of £10bn.
Since the end of its financial year in September, Impax's assets have grown further to reach £38.9bn at the end of October.
The company's profits before tax increased by 174 per cent to £45.7m while revenue increased by 63.5 per cent to reach £143m.
There has been a general boom in ESG investing taking place across the investment industry. Of the 80 exchange-traded funds and mutual fund launches in the UK in the first half of 2021, 37 were ESG vehicles.
Meanwhile data published by the Investment Association showed ESG funds attracted two thirds of UK fund flows in September, as investors pumped £1.6bn into these vehicles.
Ian Simm, chief executive of Impax, said: "Impax continues to be well positioned to benefit from many regulatory, policy, market, and investor tailwinds.
"We believe that the focus on climate change at COP26 and the post-pandemic fiscal boost will help catalyse further investment in companies benefitting from the transition to a more sustainable economy."
Sally Bridgeland, Impax's chairman, said she was "delighted" with the progess the company was making at expanding in the US market following its acquisition of Pax World Management in 2018.
She said: "We have expanded to ensure that we have the necessary resources to match ever-increasing client demand. By the end of the period the team had grown by 24 per cent, with hires across the investment management, client services and corporate services teams.
"We are also delighted with the progress of the integration of our New Hampshire-based business, which has helped further establish Impax in the strategically-important North American market."