The deal, which will support ISN's plans to open a new office in Aberdeen, signals the boardroom return of Nessco founder Tom Smith.
Mr Smith, who built Nessco into a global provider of telecommunications to the oil and gas industry before going on to sell it to RigNet in 2012, has joined ISN as chairman.
ISN, which employs about 50 staff, turns over nearly £6m by providing consultancy, project management and IT services to the oil and gas sector. The combination of Maven's investment expertise and Mr Smith's experience has been billed as holding the key to ISN's growth strategy.
The plans to open a base in Aberdeen are aimed at positioning ISN at the heart of the oil and gas supply chain, with the bulk of its clients to date based in London and south-east England.
Mr Smith said: "ISN Solutions is clearly a leading player in the field of IT systems and support to the oil and gas sector.
"I am very impressed with its management, overall capability and existing client-base and am looking forward to working with the team to assist them in their exciting growth journey."