Ojjeh was born in 1952, the son of Syrian-born Saudi businessman Akram Ojjeh, who had founded Techniques d'Avant Garde (TAG), an investment company focused on advanced technologies and headquartered in Luxembourg. His father's firm brokered major commercial and defence deals between Saudi Arabia and France. Ojjeh's mother was French, and he spent much of his childhood in France, attending the American School in Paris. He graduated in 1974 with a degree in Business Administration from Menlo College in California and later obtained a master's degree from Santa Clara University.
After graduating, Ojjeh was named chief executive of TAG Group, the company his father had built. The group operated across motor racing, aviation and watchmaking. In 1985 Ojjeh acquired Swiss watchmaker Heuer, which became the foundation of the TAG Heuer brand; LVMH purchased the brand in 1999 for 740 million dollars. TAG also at various points owned Farnborough Airport and a 10 percent stake in the upmarket jewellers Asprey and Garrard.
Ojjeh's entry into motorsport came after he watched the 1978 Monaco Grand Prix as a guest of the Saudi royal family, which was connected to Saudia, then a Williams sponsor. The experience converted him into a committed racing enthusiast. He brokered a sponsorship deal between TAG Group and Williams, and in 1979 TAG secured the principal sponsorship slot. The capital TAG brought in enabled engineering director Patrick Head to develop the Williams FW07, which proved highly competitive. Under Ojjeh's sponsorship Williams produced two world champions: Alan Jones in 1980 and Keke Rosberg in 1982.
In 1981 Ojjeh met Ron Dennis, then leading the McLaren operation, who persuaded him to become a partner. Ojjeh agreed and became the majority stakeholder in the McLaren Group, taking a 60 percent share. A pivotal early decision was the joint investment in a turbocharged engine developed by Porsche, badged under the TAG name. The TAG Porsche engine debuted in 1983 at the Dutch Grand Prix and powered McLaren to extraordinary dominance in 1984: the team won 12 of 16 races, with Niki Lauda beating team-mate Alain Prost to the title by half a point. Prost claimed the title in 1985 and again in 1986. TAG engine usage ended after 1987 when McLaren signed with Honda.
The Honda era brought further success. McLaren won four consecutive constructors' titles from 1988 to 1991, with Ayrton Senna claiming three drivers' championships and Prost one. After the Honda partnership ended in 1993, McLaren moved through Ford, Peugeot and eventually Mercedes. The Mercedes era produced another constructors' championship and three drivers' titles: Mika Häkkinen won in 1998 and 1999, and Lewis Hamilton in 2008.
In 2000 Daimler AG exercised an option to purchase 40 percent of the TAG McLaren Group, leaving Dennis and Ojjeh each with 30 percent. Both later sold half their remaining stakes to the Mumtalakat Holding Company of Bahrain in 2007. When Daimler sold its McLaren shares in 2010, Mumtalakat, Dennis and Ojjeh divided the returning stake among themselves.
Ojjeh's partnership with Ron Dennis, which had been commercially productive for nearly three decades, grew strained as McLaren's on-track form declined in the 2010s. Tensions surfaced publicly in 2014 when, while Ojjeh was hospitalised with lung disease, Dennis removed team principal Martin Whitmarsh and terminated the contract of Sergio Pérez — both decisions opposed by Ojjeh. In 2015 Ojjeh intervened to ensure Jenson Button retained his seat alongside Fernando Alonso rather than Kevin Magnussen, as Dennis had preferred. Dennis stepped down from McLaren in 2016 and subsequently sued Ojjeh and Mumtalakat, unsuccessfully.
In late 2013 Ojjeh underwent a double lung transplant after several years living with idiopathic pulmonary fibrosis. He returned to full health in 2014. He died on 6 June 2021 at the age of 68. McLaren Racing honoured him by inscribing his name on the McLaren MCL35M and on team caps at the 2021 French Grand Prix.
Mansour Ojjeh's financial commitment and business relationships gave McLaren the resources to compete at the highest level across four decades. The TAG Porsche engine, his first major investment in the team's hardware, remains one of the most successful customer powertrains in Formula One history. His long stewardship of a McLaren shareholding, and his willingness to intervene in team decisions even when unwell, reflected a level of personal investment that went well beyond that of a passive investor.