Hasler spent a season with Hull FC in England, returning to Manly, before finishing his playing career with the Western Suburbs Magpies.

Hasler began his first-grade career with the Penrith Panthers in 1982, but quickly transferred to the Manly Warringah Sea Eagles.

He played 13 State of Origin matches for New South Wales (seven from the bench, three at halfback, two at five-eighth and 1 at lock), scoring two tries during these games.

His biography, The Utility Player, was written by prominent Australian author and Manly Warringah fan Thomas Keneally and was published in 1993.

[5] Hasler also played in twelve test and World Cup matches for Australia between 1985 and 1991, with his utility value seeing him start nine of those games from the bench.

In 1990 he was largely Bob Fulton's utility player with Hasler not only selected on the bench for all three Ashes series tests against Great Britain (though no bench players were used in the 2nd test at Old Trafford), but he played a variety of positions on the tour including lock, halfback and even out on the wing.

He played 21 games for Western Suburbs alternating between halfback, lock, hooker and the bench, before retiring at the end of the season.

The team was a contender in the 2007 National Rugby League premiership, and finished second on the NRL ladder, losing the grand final 34–8 to the Melbourne Storm.

[6] In 2008, Hasler was named the Rugby League International Federation's Coach of the Year at the RLIF Awards.

[11] He had immediate success as he took the club to finish eight places better than the previous season to the top of the ladder and collected the minor premiership.

On 1 December 2017, it was announced that Hasler was taking Canterbury to court and was seeking $2 million in damages after he was terminated by the club despite signing a two-year contract extension earlier in the season.

Canterbury issued a statement saying "After a great deal of discussion over the last couple of months, the Bulldogs are pleased to have reached an agreement with Des Hasler.

[17][18] Hasler guided Manly to the second week of the finals series in 2019 as the club were defeated by South Sydney 34–26 in the elimination semi-final at ANZ Stadium.

[24] Hasler would lose his opening six games as Gold Coast head coach before finally earning his first win in charge of the club against the New Zealand Warriors in round 8.

The Gold Coast also recorded the biggest victory by a team running last across the 114-year history of top-flight rugby league in Australia.