A retirement savings platform which previously secured backing from Legal & General will this week unveil a $95m (£76m) fundraising led by a New York-based private equity investor.
Sky News has learnt that Smart, which was founded in 2014, will announce the capital raise on Monday.
It will be led by Aquiline Capital Partners, which manages over $9bn in assets and specialises in backing financial services and technology companies.
The funding deal will be one of the largest struck by a UK-based fintech this year amid a more difficult financing environment for early-stage - often loss-making - start-ups.
Sources said the proceeds of the round would be used to finance a number of impending acquisitions.
They will also accelerate Smart's investment in and distribution of its proprietary retirement savings technology platform, Keystone.
Smart's existing investors, which include Chrysalis Investments, Fidelity International Strategic Ventures and Barclays, also participated in the round, the sources said.
The company was founded by Andrew Evans and Will Wynne, and launched in 2015 in anticipation of huge demand from companies ahead of a final Government deadline for auto-enrolment in 2018.
It owns and operates one of the four major UK auto-enrolment master trusts - Smart Pension - which serves more than one million savers and 70,000 employers.
Smart's growth has been fuelled in part by the growing regulatory requirement for individuals to save for retirement at the same time that ageing populations place greater pressure on government finances around the world.
As part of the funding round, Charles Janeway of Aquiline is joining Smart's board as a non-executive director.
One insider said the capital injection had taken place at only a modest discount to its most recent fundraising.
Smart has over £5.5bn in assets under management and expects this to exceed £10bn in the near future.
It has significant international ambitions, having already struck partnerships with institutions in Ireland and part of the giant Zurich Insurance Group.
In response to an enquiry from Sky News, Mr Evans and Mr Wynne claimed that Smart was "the global leader in retirement technology, and our industry-leading platform, Keystone, is being deployed by the biggest, most successful financial institutions around the world".
"This is a $62trn global sector waiting to be disrupted, and we are uniquely positioned to take advantage of that," they added.
Bankers at Lazard advised Smart on the funding round.