The event began in 1923 under the name Manx Amateur Road Races, or MARC. The original rules were extensive and frequently disputed, as the definition of "amateur" proved difficult to pin down in practice. The MARC ran through 1930, when it was renamed the Manx Grand Prix. Over the following decades, the MGP established itself as one of the most prestigious amateur motorcycle events in the world, with a reputation for producing future TT stars.
Legendary riders including Freddie Frith, Phil Read, and Geoff Duke all raced at the MGP before going on to achieve fame at the TT and in international competition. Joey Dunlop, widely regarded as one of the greatest TT riders of all time with 26 victories on the Mountain Course, also competed at the MGP on a classic Aermacchi and achieved a podium finish. More recently, riders such as Martin Finnegan, Michael Dunlop, Lee Johnston, and Michael Rutter have used the MGP as a springboard to TT careers.
In 1989, Gloria Clark became the first woman to race in the MGP. Two years later, in 1991, she entered the Guinness Book of Records as the fastest lady on the TT Circuit. In 2009, Carolynn Sells became the first female winner on the Snaefell Mountain Course, claiming victory in the Ultra-Lightweight event and earning a Guinness World Record for the achievement.
The event celebrated its 100th anniversary in 2023. Traditionally a two-week affair, the MGP was reduced to a nine-day format in 2022.
The MGP is organised by the Manx Motor Cycle Club and runs under rules set by the Auto-Cycle Union, the governing body for most British motorcycle sport. The event begins with an extended practice period, during which all competitors must complete a minimum number of laps at a qualifying speed before being permitted to race. Newcomers — riders with no prior experience on the Mountain Circuit — are escorted on a controlled-speed lap by Travelling Marshals on the first evening of practice before being allowed to set their own pace. During practice, newcomers must wear coloured bibs over their leathers to identify themselves to other riders, and classic class riders wear white bibs.
The event consists of six races of three or four laps each. Classes for 2024 included the Lightweight Manx Grand Prix, Classic Senior, Classic Junior, Junior, Senior, and Classic Superbike. Unlike the TT, the MGP does not include a sidecar class. A Classic TT category for historic racing machines was added in 2013 as part of the Manx Government's Festival of Motorcycling initiative, which also opened some races to more experienced riders for the first time.
Because of the demanding length and nature of the course, bad weather can delay or reschedule races, and race distances may be shortened by organisers when conditions require it.
One of the MGP's defining features is its dedicated Newcomers class, which caters exclusively to riders who have no previous experience racing the Mountain Circuit. No equivalent class exists at the TT, making the MGP the only competition venue where a rider can contest their first laps of the course in race conditions. Machines in the Newcomers class are restricted to a capacity not exceeding 750cc. The class is typically oversubscribed, reflecting the demand from up-and-coming road racers seeking to prove themselves on the Mountain Course.
The Manx Grand Prix distributes approximately 42 awards each year. The event is funded entirely by entry fees and donations, reflecting its amateur roots. The winner of the Junior Manx Grand Prix receives the Douglas Pirie Trophy, while the Senior Manx Grand Prix winner is awarded the A.B. Crookall Trophy — with the notable tradition that the A.B. Crookall Trophy can be won only once, as the Senior winner is then expected to step up and enter the Isle of Man TT.
All finishers who complete the race within 110% of the winner's time receive a Finisher's Replica, a practice that recognises competitive completion of the demanding Mountain Course regardless of finishing position.
The Manx Grand Prix occupies a complementary position to the TT in the Isle of Man's motorsport calendar. Where the TT is a professional event drawing international factory-supported riders, the MGP deliberately focuses on amateurs and newcomers. Riders who achieve success at the MGP and go on to enter the TT are subject to regulations limiting their participation in the modern classes of the TT, often restricting returning MGP veterans to vintage or classic categories. The MGP is widely seen as having a more relaxed atmosphere than the TT, and it draws a loyal following of motorcycle enthusiasts who value its unpretentious character and its role in sustaining road racing's amateur tradition.