As a lawyer, he practiced for the U.S. Department of Justice and later as a public defender in Washington, D.C. Among poker players he is known as the author of the books Cappelletti on Omaha, The Best of Cappelletti on Omaha, Poker at the Millennium and How to Win at Omaha High-Low Poker, and also as columnist for the poker magazine, CardPlayer. He is well known among bridge players as the inventor of the Cappelletti convention. Cappelletti was an American Contract Bridge League (ACBL) Grand Life Master with more than 24,000 masterpoints. He won a bronze medal in the 1974 World Mixed Teams. Cappelletti also authored the book 100 Bridge Problems: Using Poker Tactics in Contract Bridge.
Cappelletti made some contributions to bridge bidding including Cappelletti over notrump, Cappelletti over one-of-a-major doubled, Cappelletti two-suited cuebids.