The financial agency is stepping up its digital offering with the investment in cubaka, founded in 2009 by Simon Rutherford, former Toyota head of digital.
As part of the deal Tony Langham, Lansons chief executive, will take a position on the cubaka board, while the agency will relocate to Lansons offices but maintain its independent branding.
Langham explained: 'All of our campaigns include social media, but there are also social media only briefs and we weren't in the market to win those and neither are most of the other top 25 PR agencies under their own identities.'
He added that the investment allows the agency to attract a higher quality of social media strategist than creating a social media function in-house.
Rutherford said the tie-up would 'offer clients the chance to plan effective social media strategy, web development, community management and crisis comms management together so that they work cohesively.'
Cubaka will continue to service its own clients as well as offer specialist digital consulting to Lansons' clients and help drive new business.
Clients at the six-strong agency include Toyota, Lexus and Davina Peace.
The news comes four months after Lansons bought public affairs consultancy Foresight Consulting.
Langham said that the agency remained interested in making another tactical acquisition in the digital space.