Nicknamed "ABBA", Abernethy was recruited from South Australian Amateur Football League (SAAFL) club Rosewater and debuted for Port Adelaide Football Club in the SANFL as a 16-year-old in 1978 and quickly made his mark as a running player of the highest calibre.
His club Best and Fairest win in 1987 and his key role in his second trifecta of Port Adelaide premierships from 1988 to 1990, including a Jack Oatey Medal winning performance in the 1988 Grand Final, ensured that recruiting scouts continued to entice him to return to the VFL.
After his football career, Abernethy became a boundary rider for the Seven Network's AFL coverage in Adelaide.
Abernethy then became the main sports presenter at Channel Seven in the early 1990s and presents the sports report on Seven News on Mondays, Thursdays and Fridays, and on weekends to maximise his coverage of weekend AFL.
Abernethy also acted as a presenter during Seven's coverage of the 2000 Summer Olympic Games in Sydney.