Dymock made his first class debut in 1971-72. A highlight was 4-34 against South Australia. The following season he took 24 wickets at 26.08.

1973–74: International debut

He had a very strong domestic season in 1973-74 with 51 wickets at 19.88. He made his test debut that summer against New Zealand, in the third test in Adelaide, replacing Tony Dell. Australia's selectors were trialling many new players and Dymock debuted alongside Alan Hurst and Ashley Woodcock; he took 2-44 and 5-58 and Australia won by an innings and 57 runs.

1974 Tour of New Zealand

Dymock was picked on the 1974 tour of New Zealand. In the first test he took 3-77. Things were harder in the second test, Dymock going for 3-59 and 0-84; his second innings effort was considered particularly disappointing as New Zealand won their first test against Australia. Dymock was dropped for the third test.

1974–75 season

Dymock began the 1974-75 season as a front-runner for test selection. He took 20 wickets at 16.8 early in the summer including five wickets against the touring English. side. However the selectors preferred Lillee, Jeff Thomson and Max Walker. Dymock took 46 first class wickets at 23.95 that summer.

He was picked for the 6th test, when Jeff Thomson was injured. Dymock went for 1-130 as Australia lost by an innings.

1975–76 and 1976–77

Dymock had a slower season in 1975-76 with 22 wickets at 31.86, and could not force his way into the test team past Lillee, Thomson, Walker and Gary Gilmour. However the following summer he took 34 wickets at 24.65, including 5-24 against South Australia, earning him a spot on the 1977 Ashes in place of Gilmour.

1977 Ashes Tour

While in England, it was revealed he was one of our four tour members who had not been offered a spot with World Series Cricket. He was offered the chance to play cricket in Tasmania but turned it down when he was offered sponsorship from radio station 4IP (who were also sponsoring Gary Cosier and Thomson). Dymock took 15 first wickets at 31.20 on tour but was the only pace bowler who did not play a test..

World Series Cricket

1977–78

Dymock was ignored for national selection during the 1977-78 summer, not picked to play any tests against the touring Indian side and overlooked for the tour of the West Indies.

1978–79

However he began the 1978-79 series well, with 5-45 against Vic