Lipner is professor of law at the Zicklin School of Business of Bernard M. Baruch College in New York City. He teaches graduate and undergraduate courses in, among other subjects, law and international business, negotiation and dispute resolution, and law and e-business. Since 1985, Lipner has also been a member of Deutsch & Lipner, a law firm in Garden City, N.Y., where he represents investors with grievances against providers of financial services. Since 1987, with some exceptions, these cases have been heard in arbitration.

Lipner writes frequently on securities arbitration, securities regulation, and the securities industry, and speaks regularly to bar groups and at continuing legal education programs. He is the author of numerous scholarly articles and law books on diverse fields including international trade law, securities arbitration, and law and technology. Lipner was among the founders of the Public Investors Arbitration Bar Association (PIABA), and he served as president in 1994–95 and again in 2000–01. He also served on the National Arbitration and Mediation Committee of the National Association of Securities Dealers (NASD) between 1999 and 2003. His ideas and comments on NASD and New York Stock Exchange rulemaking proposals are often cited by the Securities and Exchange Commission and the self-regulatory organizations as influential in the governance of securities arbitration.