Manwaring was a racing fan in his childhood. He was brought up in the comfortable suburbs of south London and after school enrolled to study mechanical engineering at Sussex University in Brighton. His route from home to college took him passed the headquarters of the Surtees F1 team in Edenbridge and, having abandoned his own racing career because he did not have enough money and crashed too often, Manwaring started working at Surtees in his university vacations. When he graduated, aged 21, Manwaring got a job as a draughtsman in the Surtees design office but after three months a job came up as spares man for the race team and Rupert took it, preferring to travel to the races rather than sit around a drawing office.A year later he was assistant team manager to John Surtees, but the team was in difficulties and when it closed down he moved to Brabham to work as a stores coordinator. He stayed for six years, rising to assistant team manager under Bernie Ecclestone and Herbie Blash. During that time Nelson Piquet won two World titles for Brabham.In 1984, feeling the need for a change, Manwaring quit Brabham and went to work for the Kraco Indycar team, based at Knaphill in Surrey, England. The job lasted only a few months before he was back in F1 as assistant team manager to Tyler Alexander in the Haas Lola FORCE team. The team folded in 1986 after its main sponsor Beatrice pulled out of F1 and Manwaring moved on to Team Lotus where he became assistant team manager to Peter Warr, working with Ayrton Senna and later with Piquet again. Finally, in 1989, he emerged from the shadows to become Lotus team manager. A year later he was recruited by Tyrrell and he then spent four years as team manager before being appointed head of the Tyrrell marketing department in 1995.He stayed with Tyrrell until the middle of 1998 - the Tyrrell Family had by then sold the team to British American Tobacco - when he joined Harvey Postlethwaite's Honda Racing Developments operation. After Postlethwaite's death in early 1999 Manwaring took over the running of the team but Honda decided it should be closed down.Manwaring came close to joining Benetton but in the autumn of 1999 fronted a consortium which was trying to buy control of the Arrows F1 team. It failed, but in 2001 he became team manager of Minardi when Australian Paul Stoddart took over. At the end of 2002 he left the team to become managing-director of Lola Cars International.