Thomson had an unusual but highly effective slinging delivery action that he learned from his father. In December 1975, after the second test match against the West Indies at the WACA, he was timed with a release speed of 160.45 km/h using highly accurate, high-speed Photo-Sonics cameras. The study was carried out by Tom Penrose and Brian Blanksby of the University of Western Australia, and Daryl Foster of the Secondary Teachers' College in Perth. Measurements were also made of three other fast bowlers, Dennis Lillee, Andy Roberts and Michael Holding, and the study is described in Dennis Lillee's book, The Art of Fast Bowling.

Thomson's fastest delivery was significantly quicker than the next fastest bowler, Andy Roberts, whose fastest delivery was measured at 150.67 km/h. Another interesting finding from the study was the run-up speed of the bowlers. Thomson approached at 18.02 km/h, significantly slower than Holding (28.10 km/h), Roberts (28.78 km/h) and Lillee (33.57 km/h). When Thomson bowled one of his 160 km/h deliveries it is calculated that the ball took a mere 0.438 seconds from leaving the bowler's hand to reaching the bat. Studies have shown that it takes about 0.30 seconds for a batsman to see the ball, predict its path and decide on a stroke, and a further 0.30 seconds to perform the stroke. This suggests that a batsman would need to start his reaction time 0.162 seconds before Thomson released the ball, or start to play the stroke before knowing where the ball would pitch.

In 1979, Thomson won a fastest bowling competition held by the Australian television station Channel 9, in a year in which he was banned from playing professional cricket. His maximum speed was timed at 147.9 km/h using the same method as employed during the 1975 study at the WACA. He also came top for accuracy in the competition.

Most cricketers, experts and viewers who have watched cricket from at least the 1970s rate Thomson as the fastest they have ever seen. Richie Benaud rated Thomson as the fastest he had seen since Frank Tyson. Australian wicket-keeper Rod Marsh kept wicket to Thomson for most of his Test career and has claimed that Thomson bowled upwards of 180 km/h. Ian Chappell and Ashley Mallett have also opined the same.

Many of the players of the 1970s and 1980s generation also rate Thomson as the fastest they ever faced or even saw. West Indian batting legend Viv Richards, rates Thomson as the fastest he has ever faced. Richards' opinion counts for a lot, as he faced almost all the fastest bowlers of all time through the 1970s and 1980s in John Snow, Dennis Lillee, Andy Roberts, Imran Khan, Michael Holding, Sylvester Clarke, Wayne Daniel, Malcolm Marshall, Patrick Patterson, Alan Ward, Len Pascoe, Garth Le Roux, Graham Dilley etc, and even Devon Malcolm and Waqar Younis in the early 1990s, at various levels, in International matches, the WSC, and the Caribbean, Australian and England County leagues.

Indian batting great Sunil Gavaskar also reckons Thomson was the fastest he faced over a career spanning over 20 years. Former West Indies captain Clive Lloyd regards Thomson as the fastest bowler he has ever seen. Michael Holding, himself often considered an extremely fast bowler in his prime, believes Thomson to be the fastest he ever saw. Geoffrey Boycott rates Thomson joint fastest with Michael Holding among all the bowlers that he has seen.