Nunn gave up his driving career in the late 1960s to build Formula 3 cars. He eventually built his first Formula 1 car for Ricky Von Opel in 1973. This led Nunn to form his own Formula 1 team to build and race cars under the Ensign name. Ensign fielded a Formula 1 team for 10 years.
Morris Nunn came from a family of car dealers. He broke into motor racing by accident when he saw a Cooper-Climax in a showroom and decided to buy it. He spent 1963 and 1964 racing the Cooper and a Lotus sportscar.
Then in 1965 he found backing from Bernard Lewis and entered F3 with an old Lotus entered by Lewis-Nunn Racing. The team added a second car in 1966 for Ken Crook. Nunn won at Mallory Park in May and other results followed, encouraging him to test himself against Eurpoean opposition at Albi at the end of the year. He finished a respectable fourth.
Running a privateer Lotus 41 in 1967, he won several races which earned him sponsorship from Astrali Accessories for the 1968 season.
Team Lotus also took notice and in 1969 he was given a works drive in F3 alongside Roy Pike with occasional F2 outings. At the end of the year he looked to make the move to Formula 5000 but this fell through.
Nunn wanted to build his own car and with support from Lewis he built a prototype Formula 3 car, the LNF1, in a garage behind his house in Walsall. Finished in November 1970, it was tested that winter and raced for the first time in the first round of the British F3 series at Brands Hatch in March 1971 with Bev Bond finishing a fine second. It won the second and third rounds and a second car appeared for Steve Thompson in May.
Later in the year Bond's car was sold to David Purley's Lec Refrigeration Team and a third car was built for Mike Walker. The cars were so successful that there was no shortage of customers in 1972. Team Ensign ran Walker and Rikki von Opel in LNF3 chassis and several customer cars including David Purley and Colin Vandervell. They was also built an F2 car, the LNF2, driven by John Burton without success.
Rikki von Opel commissioned Nunn to build a Formula 1 car for 1973. Dave Baldwin joined the team to work on F3 customer cars and Nunn designed the N173. It made its debut at the French GP and raced six more times that year, failing to score any points. The 1974 car was a revised version of the N173 but von Opel left to join the Brabham factory team, and Ensign were left struggling.
Nunn continued with Ensign and though the cars were ofter quick, results never came.
1980 looked promising. With Unipart sponsorship and Clay Regazzoni driving, he was running fourth at Long Beach when he crashed, suffering serious back injuries. The team never recovered and the end of 1983 Nunn sold the team to Teddy Yip and moved to America to work with Bignotti-Cotter running Robert Guerrero in Indy cars. Guerrero finished second in the Indianapolis 500 that year.
He then joined Newman Haas Racing before moving to Patrick Racing in 1989. He oversaw Emerson Fittipaldi's CART title winning season, which included victory in the Indianapolis 500.
In 1992 he joined Ganassi Racing and oversaw four consecutive CART titles, first with Jimmy Vasser in 1996, then Alex Zanardi in 1997 and 1998 and finally with Juan-Pablo Montoya in 1999.
At the end of 1999 Nunn set up Mo Nunn Racing with partners Bruce McCaw and Rod Campbell running a Reynard-Mercedes for Brazil's Tony Kanaan. However running his own team did not prove so successful. Like Ensign, the team was often under-funded. In their debut season, Tony Kanaan failed to post a top-5 finish. A second car was added for Alex Zanardi in 2001, but he suffered a horrific crash at the Lausitzring in which he lost his legs. Kanaan finished the championship in the top 10.
In 2002 Mo entered both the ChampCar and the rival Indy Racing League championship. With more success in the IRL with Felipe Giaffone, the team deceided to concentrate solely on the IRL in2003. With Toyota and Pioneer backing the former F1 driver Tora Takagi joined the team. He finished 10th in the 2003 standings, while Giaffone missed races through injury. His replacement Alex Barron was a race winner however.
For 2004 only one car was entered, for Takagi, whose performance was not impressive after a heavy crash at Twin Ring Motegi. Other than the 2005 Indy 500, Mo has not been involved in racing since.