Juan Roig was born on 8 October 1949 in Valencia. He studied in a Jesuit school in Valencia, then at a boarding school, and graduated in economics at Valencia, but was not an outstanding student. Eight years after graduating, he studied a postgraduate at IESE Business School, University of Navarra.

At university he met Hortensia Herrero, and they married in 1973. They have four children, and live in Valencia, Spain. His wife is now vice-president of Mercadona. He is said to favour family ownership in business, provided that the family members contribute positively.

With three of his five brothers, Juan Roig bought the shops from his parents in 1981. He largely bought out his brothers in 1991, and went on to build up the Mercadona supermarket chain, which now runs over 1,400 stores. His success in retail has been based on a risky strategy of competitive pricing, and on technological innovations such as barcode scanners and automated distribution facilities. He introduced full-time contracts for all employees in the late 1990s.

Roig was awarded the Prince Felipe Prize for Business Excellence in 2010.

Forbes magazine in October 2013 reported that Roig was worth 5,800 million euros, the second largest fortune in Spain. This in fact is the estimated value of the 78% stake in Mercadona jointly owned by himself and his wife. But since Mercadona shares are not publicly quoted, the figure is somewhat speculative. As of July 2018, Forbes estimated his net worth at US$4.3 billion. The shareholding yielded dividend income totalling over $400 million between 2006 and 2013 for Roig and his wife jointly.