[7] At the British U20 championships in August 1984, Thomas finished 2nd in the 400 m.[8] He debuted in the 800 metres in September 1984, running 1:55.3.

[1][10] Following a stint for the Iowa State Cyclones track and field team in the U.S., Thomas returned to Liverpool in 1987.

[11] Thomas competed at his first continental championship in 1987, placing 4th in his heat at the European Indoor Championships 400 m.[2] Later that year, Thomas was selected for the British team at the 1987 World Championships in Athletics, set to compete in the 4 × 400 m.[12][13] Thomas led off his team to a heat win and runner-up position in the semi-finals, but him and Todd Bennett were both substituted out by Derek Redmond and Roger Black in the finals.

[2][16] Thomas qualified for the finals of the 1990 European Champion Clubs Cup, but he did not compete due to work obligations at the Liverpool J.M.

Thomas disliked travelling internationally for competitions due to the cold weather, and he spent most of his time in Liverpool.