In 1980, Balazs was hired by David Garth Associates to serve as Press Secretary to Bess Myerson, a Democratic candidate for Senator from New York State. Balazs co-founded Biomatrix with his father in 1988. The biotechnology company developed six hyaluronan products before it was sold in 2000 to Genzyme for an estimated $738 million. Between 1988 and 1989, Balazs invested in various projects including the Manhattan nightclub M.K. and the Los Angeles supper club b.c. In 1989 he purchased The Mercer Hotel property in SoHo, a 100-year-old manufacturing loft. In 1990, Balazs purchased and restored the Chateau Marmont. Built in 1929 and located on Sunset Boulevard, Balazs reportedly paid just over $12 million. In 1997, he purchased and updated the Sunset Beach Hotel and Restaurant on Shelter Island. The following year, Balazs opened the redeveloped Mercer Hotel and Mercer Kitchen in SoHo. In 1998, Balazs opened the first of five hotels called The Standard in West Hollywood. Balazs subsequently opened and operated five Standard hotels: in Hollywood, Downtown Los Angeles, Miami, and two in New York City, before selling his interests in the real estate, and in the management company in 2017. Balazs has placed a strong focus on the culinary programs for each of his properties. The restaurants at the properties include the Standard Grill at The Standard, New York; The Lido Restaurant and Bayside Grill at The Standard Spa, Miami and Sunset Beach; Bar Marmont and the terrace restaurant at Chateau Marmont with Carolynn Spence; and The Standard Biergartens in New York and Downtown LA with Kurt Gutenbrunner. In 2007, Balazs began a collaboration with Wölffer Estate Vineyard on Long Island to create his own vintage of rosé. In 2011, Balazs launched a sea plane service to the Hamptons from Manhattan. In 2012, Balazs started The Farm at Locusts-on-Hudson on the grounds of the former Astor family estate he purchased in Hyde Park, New York, to grow organic produce for his New York restaurants. He also owns the Chiltern Firehouse, a hotel in a former fire station in London. Chiltern Firehouse was designed in conjunction with Studio KO, though Balazs is known to be personally heavily involved in the design of his hotels and it includes bar areas, a restaurant and suites. Balazs has also been involved in residential real estate as the developer of 15 William, condominium in New York City's Financial District.
Balazs married Katie Ford on November 16, 1985; they divorced in 2004. They have two daughters, Alexandra and Isabel. He was engaged to actress Uma Thurman between 2004 and 2007, and the couple again dated from 2015 to 2016. He also had a relationship with comedian Chelsea Handler from 2011 to 2013. His girlfriend, Cosima Vesey, the daughter of Sita-Maria de Breffny and Thomas Eustace Vesey, 7th Viscount de Vesci, gave birth to a son with Balazs, Ivo Vesey, on July 9, 2017. In 2017, the New York Times reported allegations that Balazs had "groped" Amanda Anka in London at a dinner hosted by him for Jennifer Aniston and Justin Theroux. A statement issued by Amanda Anka and her husband, Jason Bateman, said that "his actions were dealt with at the time."