Haymarket Network, part of Media Week owner Haymarket Media Group, was appointed to launch the monthly Sky Sports magazine in January 2007.
The magazine is circulated to more than four million subscribers to the Sky Sports pay-TV channels.
Four of the seven Haymarket Network staff who worked on the title, across commercial and editorial, have transferred across to BSkyB. The other three staff have remained within the Haymarket Group.
A BSkyB spokesman said the decision was taken following "a review of how best to resource the magazine in the longer term, in light of an expanding in-house editorial and production capability".
Andrew Taplin, managing director of Haymarket Network, said: "Haymarket is very proud of its close working relationship with Sky in the creation and development of Sky Sports magazine over the past three years."
Sky Sports magazine joins Skymag, aimed at all BSkyB satellite TV customers, which was brought in-house last year after its former publisher, News Magazines, was shut down by parent News Corporation.
Sky Movies magazine is currently produced by Future Plus, the contract publishing arm of Future.