The Senior TT first ran in 1911, when the TT moved from the shorter St John's Short Course to the full Snaefell Mountain Course. That inaugural Senior race was open to 500 cc single-cylinder and 585 cc twin-cylinder motorcycles. American-built Indian machines proved particularly well suited to the demanding mountain circuit, and Oliver Godfrey won the first Senior TT at an average speed of 47.63 mph over five laps of the new 37.40-mile course.
From 1912, the Senior TT was restricted to 500 cc machines, a capacity limit that remained in place until 1984. The class subsequently evolved through several capacity changes: 1,000 cc four-strokes were allowed in 1985 and 1986, the limit expanded to 1,300 cc in 1987 through 1989, then was reduced to 750 cc for the period 1990–1998, before the current 1,000 cc four-stroke limit came into effect.
The Senior TT was part of the FIM Motorcycle Grand Prix World Championship from 1949 to 1976. The longest race distance for a FIM World Championship event was the 1957 500 cc TT, contested over eight laps covering 302 miles, won by Bob McIntyre riding a Gilera in 3 hours, 2 minutes and 57.0 seconds at an average race speed of 98.99 mph. Safety concerns prompted the FIM to remove the Isle of Man from the World Championship calendar after 1976, with the British Grand Prix subsequently held at circuits on the mainland.
The Senior TT operates as an open-class race for the largest and most powerful machines at the TT. Modern eligibility encompasses TT Superbike machines complying with FIM Superbike specifications, Supersport-specification machines, and Superstock-specification entries. Riders must hold a valid National Entrants or FIM Sponsors Licence for Road Racing. The official qualification standard requires a lap time within 115 percent of the time set by the third fastest qualifier in the class.
The lap record for the Senior TT stands at 16 minutes and 42.778 seconds, an average speed of 135.452 mph (217.989 km/h), set by Peter Hickman during the 2018 Senior TT Race. The race record, also held by Hickman from the same 2018 event, is 1 hour, 43 minutes and 8.065 seconds, representing an average race speed of 131.700 mph (211.951 km/h) over six laps of the Mountain Course.
Through most of its history the Senior TT was cancelled only during the two World Wars and in 2001 due to travel restrictions connected with the foot and mouth outbreak. The 2012 edition was cancelled for safety reasons following inclement weather, ending a long run of continuity outside wartime. The 2020 and 2021 events were cancelled due to the COVID-19 pandemic.