Since leaving motorsport, Diniz founded the Formula Renault 2.0 Brazil Championship which he ran from 2002 and 2006, later becoming a partner in Pão de Açúcar and operates an organic produce and dairy farm alongside his wife Tatiana Diniz. He is a Board Member of Food Tank, a non-profit organization that spotlights environmentally, socially, and economically sustainable ways of alleviating hunger, obesity, and poverty and works to create networks of people, organizations, and content to push for food system change.
Diniz was considered a pay driver during his career, but was one of the few to score points in Formula One (ten during a time when only the top six drivers earned points).
Diniz began karting at the age of eighteen, and his career was funded by his father who supported his son's hobby. He competed in several events around Brazil and his first racing success came when he won the Two Hours of São Paulo. Aged 19, Diniz moved up into car racing, competing in the Brazilian Formula Ford championship, where he finished ninth in the Drivers' Championship. In 1990, Diniz moved to the Reyanud Alfa team and finished ninth overall, with his best performances being a podium position at Interlagos.
For 1991, Diniz moved to the British Formula 3 with the West Surrey Racing team, finishing 11th overall. He moved to the Edenbridge Racing team in 1992, driving a Reynard Mugen and took two podiums en route to eighth place overall.