The Haymarket monthly appointed the agency after a three-way pitch. Praxis replaces incumbent agency, Wales-based Strobe.
Strobe worked with Stuff and fellow Haymarket magazine What Hi Fi? for five years, but Stuff associate publisher Emma Lees said they wanted a London-centric agency.
'We decided we wanted to achieve more direct marketing and targeting of potential readers who are London-based or conurbation-based,' she added.
Praxis MD Ruth Reynolds heads a team of three on the brief, reporting to Lees.
Lees said: 'The number one aim is to increase the readership, but we also want to build the brand - we want to be seen as experts on consumer electronics in the industry and among consumers.'
Praxis will also work on promoting 'Stuff Live 2002', an event in October.
The agency already works for Haymarket titles F1 Racing, Autosport and rallyXS.