Sullivan & Cromwell is advising Chinese ecommerce giant Alibaba Group Holdings Ltd. on a $1 billion investment in Southeast Asian peer Lazada Group.

In its largest overseas investment to date, Alibaba will pay $500 million for new shares in Lazada and another $500 million for shares owned by existing shareholders including Berlin-based startup investor Rocket Internet S.E. The Chinese company will hold a controlling 67 percent stake in Lazada once the deal completes.