Mr Lightbody joined the board of the business in early 2007 as part of its £37.5 million purchase of his Hamilton based family cake making business Lightbody Group. The following year he became chief executive before moving to the chairman role in November 2009.
Finsbury still employs around 1,100 Scottish workers at facilities in Hamilton and Twechar, East Dunbartonshire.
Last year it sold its gluten free subsidiary in West Lothian to Lucinda Bruce-Gardyne's Genius Foods in a £20m deal to help reduce debt.
Yesterday Finsbury confirmed former Maple Leaf Bakery, Rank Hovis Mills and La Fornaia Bakeries executive Peter Baker will be its new chairman from July 1.
Finsbury non-executive director David Marshall, who also had spells as chairman and deputy chairman, is also stepping down.
John Duffy, chief executive, said: "I am very pleased to welcome Peter to the group as chairman. Finsbury Food is at a pivotal stage of its evolution and we have been shaping the expertise and capabilities of the board accordingly.
"Peter's wealth of global industry and PLC experience will be a considerable asset to the group.
"I would also like to take the opportunity to thank Martin and David for their support and dedication to the group throughout the years and wish them both the very best for the future."
Mr Lightbody has 7.2 million shares in Finsbury which is equivalent to 10.95 percent of the issued share capital.
He also still heads Glasgow based Lightbody Ventures which works in licensing, manufacturing, product development and distribution in the food and drink industry around the world.
Prior to joining his family firm Mr Lightbody completed a number of qualifications in baking including at the Richemont School in Switzerland.