Gruppo Campari said it had reached an agreement with the controlling family shareholders of the French-listed company Societe des Produits Marnier Lapostolle (SPML) for the deal, worth 684 million euros ($759 million).
The move will enable Campari "to further capitalise on the revival of classic cocktails, particularly in the US", it said in a statement.
Chief executive Bob Kunze-Concewitz described Grand Marnier as "a French icon, with a rich 150-year history".
"With Grand Marnier, we add a premium and distinctive brand to our Global Priorities portfolio, thus driving richer product mix, and we further consolidate our position as the leading purveyor of premium liqueurs and bitter specialties worldwide," he added in the statement.
The French company's controlling family shareholders have agreed under the deal to hand over their remaining shares if Campari's stake ends up less than 50.01 percent after the takeover, it said.
Campari group said it was offering €8,050 per share in cash, representing a 60.4 percent premium to the current share price, it said.
The deal also includes an add-on linked to the sale of real estate in St Jean Cap Ferrat.
"Gruppo Campari has reached an agreement with the controlling family shareholders of SPML for the acquisition of a controlling stake of the company via a tender offer, to be launched on the French stock exchange market pursuant to the applicable French regulations.
"Simultaneously, the group has entered into an agreement with SPML for the exclusive worldwide distribution of the Grand Marnier spirits portfolio," it added.
In April 2014 the Italian company, which owns around 50 brands including SKYY vodka and Glen Grant whisky and distributes in 190 countries, announced it was buying the owner of the Averna digestif brand, saying it hoped for a boost from new trends in the US.