NEW YORK — The Swatch Group agreed Monday to make its largest acquisition to date, taking over the watch and jewelry business of Harry Winston, which plans to shift its focus to its diamond mining activities.

Swatch, the world’s largest maker of watches, said it would pay $750 million in cash for Harry Winston and assume $250 million of debt. The publicly traded Harry Winston Diamond Corp., based in Toronto, will be renamed Dominion Diamond after the sale is completed.