STM Group's bid to buy Carey Pensions has gone ahead after the deal was signed off by the Financial Conduct Authority.
The companies announced the deal in October, as Carey Pensions faced legal claims from an investor.
As part of the £400,000 deal, STM will buy Carey Administration Holdings, which in turn owns 70 per cent of Carey Pensions and 80 per cent of Carey Corporate Pensions.
The remaining minority interests are held by Christine Hallett, chief executive of the pension provider, who will continue in her role.
Alan Kentish, chief executive of STM Group, said: "We are delighted that Christine and her teams are joining the STM Group.
"The two UK focused pensions businesses give us some really exciting options for our growth strategy.
"I have no doubt that the support and stability of STM will allow the Carey Pensions businesses to flourish; they have solid product offerings and a loyal and professional intermediary base."
A judgement is currently pending in a court case between Carey Pensions and an investor who argued the company had a duty of care towards him when allowing him to set up a self-invested personal pension to make unregulated investments, despite the sale being classed as execution-only.
Since then a second legal challenge has been launched by a client over its alleged failure to undertake the required due diligence when accepting investments.
When the deal was announced last year, STM acknowledged the legal battle and said it has secured indemnities as well as the benefit of significant existing professional indemnity cover from the sellers.
Ms Hallett said: "We are delighted that the acquisition has now finally been completed.
"STM's vision for the UK market, both in terms of Sipps and workplace solutions, as well as their support and resources, makes STM the perfect partner for us to be able to further grow successful and profitable businesses."