Both restaurants, which have been run by administrators at Deloitte since Paramount collapsed on 25 November, will continue to be run under their current names for the next four months before being re-branded Spaghetti House.
The move will increase Spaghetti House's estate to 12 and coincides with the family-owned business's plans to refurbish its existing London sites next year.
Commenting on the deal, Peppino Esposito, group operations director for Spaghetti House, said: "This is a very exciting time for Spaghetti House. Together with our refurbishment plans for 2012, these new acquisitions will increase our presence and profile in key landmark locations, and will be offering that true, authentic Italian cooking which sets us apart."
So far, three of the 25 sites left following Paramount's move into administration, have been sold with 17 Brasserie Gerards, three Livebaits and two Bertorellis yet to find new owners.
Cafe Fish owner Richard Muir bought its Livebait site in Manchester at the end of November under his new restaurant company SBG Restaurants and eight of Paramount's Chez Gerard sites were immediately snapped up by Raymond Blanc's Brasserie Bar Co. when the company went into administration.
Spaghetti House founders Simone Lavarini and Lorenzo Fraquelli opened their first site on Goodge Street in London in 1955. The group has since expanded across the capital, opening sites across it, from Knightsbridge to the edge of the City in Holborn and a £1m site in Westfield London in 2009.