Slaughter and May and Surrey firm Stevens & Bolton have both won places alongside longstanding adviser Simmons on the new panel.
The shake-up in the Simmons relationship comes despite the fact that Gallaher's group legal counsel is former Simmons litigation partner Tom Keevil.
Keevil joined Gallaher in 2000 as group legal counsel and took on the combined role of company secretary and general counsel earlier this year. The in-house team is led by Suzanne Wise.
The vast majority of Gallaher's work has traditionally been outsourced to Simmons. The new panel appointment is a major coup for Stevens & Bolton, which is based close to Gallaher's headquarters in Weybridge. The client win is understood to boost the firm's FTSE 100 client list to three. Stevens & Bolton also acts for Hays and the BOC Group.
Gallaher is understood to have looked at a number of other firms over several months before adding Stevens & Bolton and Slaughters to its list.
Simmons advises Gallaher worldwide, with corporate partner Chris Wilkinson managing the relationship.
A Simmons spokesman said the new panel appointment was a positive step, but added that it was not yet clear how the work would be split between the three firms.
Gallaher is also known to have used Arthur Cox in Ireland, Gomez-Acebo Pombo in Spain and Chadbourne & Parke in Moscow and elsewhere.
Gallaher markets the Hamlet brand worldwide and Benson & Hedges in certain countries. It is currently working on a series of press and poster advertisements to mark the end of its advertising glory days, before the law banning newspaper, magazine and billboard advertisements for tobacco comes into effect in February next year.