Joseph is a partner at Paul Weiss and co-chair of its Antitrust Group. He was the chief antitrust enforcer at the Federal Trade Commission (FTC), serving as Director of the Bureau of Competition. Under his leadership, the Commission pursued a strong bipartisan enforcement agenda under which all but one of the more than 70 antitrust enforcement actions taken by the agency were by unanimous vote. During his tenure, the FTC prevailed in all of the 46 merger enforcement actions taken by the Commission. Along with a former chief economist of the Department of Justice Antitrust Division, Joseph developed "Critical Loss Analysis," a technique for market definition that has been adopted and used widely by the Antitrust Division, the FTC, and the U.S. Court of Appeals. In 2005-2008, Joseph was named one of America's leading antitrust lawyers in Chambers USA: America's Leading Business Lawyers.