The deal was revealed on prweek.com/uk this week. It values College Group, which encompasses City PR agency College Hill, at about £45m - around ten per cent more than the company's turnover.
Vitruvian will take a small majority stake, with existing College Group shareholders keeping the rest of the equity.
The deal brings to mind private equity firm Advent International's 2003 purchase of FD. Under Advent, FD expanded outside the UK and was sold to FTI Consulting for substantial profit in 2006.
Despite's Advent's success with FD, there have been few large-scale PE investments in the UK comms industry.
College Hill founder and College Group chairman Alex Sandberg said: 'You need investors who are not frightened of people businesses.
'Communications groups are far harder to build than anyone knows, but they are also far harder to destroy. People are beginning to realise that these businesses are not nearly as fragile as perhaps they once thought.'
One factor that has largely constricted the industry to trade deals is that few consultancies are of the scale and have the growth potential to satisfy private equity.
PE investors will typically look for businesses to grow by 20 per cent a year, and aim to exit after several years.
Tony Langham, MD of independent agency Lansons, said there could be more deals in the pipeline, as the industry is suited to PE investment.
'There is a lot of M&A activity in our sector,' he said. 'We are in an increasingly integrated world where there are bigger and bigger accounts, and PE is suited to putting together four or five brands and making them bigger together than they are separately.'
As part of the College Group deal, Sandberg will step down as group chairman, handing the day-to-day management to CEO Richard Nichols.
Nichols said the deal would enable the group to build its presence in the US, Europe and emerging markets.