Patrick Gaillard was born in Paris, where his father owned a van and truck hire business.
He started racing in Formula Renault in 1975 in a privately-entered Martini moving up to European Formula 3 in 1977 with a Chevron-Toyota and finishing fifth at Croix-en-Ternois.
In 1978 he became a works driver for Chevron driving a B43. He won at Imola and the Nurburgring and along with three seconds, he finished the year third overall in the Championship.
Gaillard came close to making a real name for himself that year when he led the Monaco Formula 3 race only to be punted off by the eventual winner, Elio de Angelis. At the end of the year he raced an F2 Chevron in Japan finishing fourth at Suzuka.
Racing full time in Formula 2 for the 1979 season he made only four starts as he stepped into the Ensign seat vacated when Derek Daly left the team after the Monaco Grand Prix. Tiff Needell had been lined up as a replacement but when he was refused his superlicence, Gaillard was recruited for the French GP at Dijon. He failed to qualify the Ensign N179 first time out but at Silverstone he made it onto the grid and finished 13th. He just missed out on qualifying in Germany but made it in Austria and was running 12th when his car suffered a suspension failure. After another DNQ at the Dutch GP at Zandvoort, Mo Nunn brought in Marc Surer as a replacement. At the end of the year he went to America and raced in CanAm at Laguna Seca.
He tried to get back into F2 with AGS in 1980 but a drive did not materialise. He made a brief return to F1 with Ensign for the Spanish GP where he finished sixth. However the race was later downgraded to non-championship status and so he lost his one World Championship point.
He returned to F2 with Maurer for two races before going to Japan to do two races for Walter Wolf. He also raced at Le Mans in 1980 driving an ACR, a car which he also drove in 1981.
At Le Mans in 1982 he raced a Cougar and in 1983 he shared a Kremer Porsche CK5 with Derek Warwick and Frank Jelinski.
After retiring he became an instructor at the AGS Racing School in the south of France.