Wigan-based Prosper will bring an additional 486 clients to IWP along with four advisers and six support staff and will form a new Northern 'hub.'
The acquisition also secures gross fee income of £1.35m and an additional £170m in funds-under-management.
The deal, for an undisclosed sum, is IWP's first in Lancashire and pushes total IWP funds under management to over £1bn.
Prosper was founded in 2003 by David Barton who will stay with the business.
IWP says Prosper will provide IWP’s main hub for the North West of England and managing director Mr Barton will continue to lead the team and any further acquisitions that IWP might make in the area.
Prosper has grown organically over the last 16 years and also acquired two smaller IFA firms more recently.
It specialises in retirement planning and has close relationships with many Wigan law and accountancy firms.
IWP businesses include Alexander Grace Chartered Financial Planners, Kelsall Steele Investment Services, Murdoch Asset Management, Rixons Wealth Management, Bartholomew Wealth Management and now Prosper.
Unusually for a consolidator, IWP retains the local businesses as separate brands and operations run by a local board of directors.
Mr Barton said: “Having previously built Prosper both organically and through acquisitions, I completely understand the logic behind the IWP model.
“I had ambitions to grow Prosper Wealth significantly over the coming years, however to achieve this I really needed more support. My personal experience of going through the acquisition process with IWP has reassured me that they have both the resources and expertise to get the deals done.”
David Inglesfield, IWP chief executive, said: “David and his team have a fantastic reputation in their local community and are a great fit for IWP. I have every faith that they will do an excellent job in growing our presence across the North West region.”