List of Adelaide United FC seasons

Adelaide United Football Club, is an Australian professional association football club based in Hindmarsh, Adelaide. The club was founded in September 2003 as they competed in the final season of the National Soccer League (NSL) as they replaced Adelaide City in the league until 2004, when they announced their team to compete in the A-League Men which was the replacement for the NSL.

History
Adelaide United were formed for the final season of the National Soccer League in the 2003–04 season finishing third place and the Preliminary Final. The first season of the A-League Men in 2005–06 saw the club win the Premiership before losing to Central Coast Mariners in the Preliminary Final. Ultimately finishing second in the league and runners-up in the Grand Final both losing to Melbourne Victory for the 2006–07 season, Adelaide United won the second edition of the A-League Pre-Season Challenge Cup, defeating the Central Coast Mariners 5–4 on penalties after a 1–1 draw and qualified for the AFC Champions League for the first time being knocked out in the group stage. Adelaide missed out on A-League Finals for the first time in their history in the 2007–08 finishing 6th, but winning back-to-back Pre-Season Challenge Cup titles by winning the Final 2–1 against the Perth Glory (the last time until seven years the club won a trophy), and becoming the first Australian club to reach the AFC Champions League Final ultimately losing 5–0 on aggregate. In 2008–09, Adelaide United was again defeated in the A-League premiership and championship to Melbourne Victory, and finishing last for the first time in 2009–10. Sergio van Dijk scored 17 goals in the 2010–11 season; the most ever in a season for Adelaide United and winning the Golden Boot as the club made third place and semi-final finish. Two further seasons of no podium finishes and elimination final knockouts in the A-League occurred for the next two seasons.

In 2014, Adelaide United won the inaugural FFA Cup (now Australia Cup) in the 2014–15 season, defeating the Perth Glory 1–0 via Sergio Cirio, winning their first club trophy in seven years. The 2015–16 season saw Adelaide United win the Double for the first time, doing so by a slow start of eight winless games and a long undefeated run (with a one game exception) towards the Premiership and winning the Grand Final 3–1 against the Western Sydney Wanderers. The Double defense season in 2016–17 had Adelaide only finish 9th and missing Finals for the first time in four years. Since 2017, Adelaide United qualified for three consecutive FFA Cups, losing in 2017 against Sydney FC 2–1 after extra time, but winning back-to-back titles after in 2018 (2–1 against Sydney FC) and 2019 (4–0 against Melbourne City and currently their last club honour). A COVID-19 affected A-League campaign in the 2019–20 season saw Adelaide miss out on finals. Since 2020, Adelaide United have finished their last three Finals series campaigns in the semi-finals.

Key
Key to league competitions:
 * A-League Men – Australia's top soccer league, established in 2005
 * National Soccer League (NSL) – The previous first tier of Australian soccer until 2004

Key to colours and symbols:

Key to league record:
 * Season = The year and article of the season
 * Pos = Final position
 * Pld = Matches played
 * W = Matches won
 * D = Matches drawn
 * L = Matches lost
 * GF = Goals scored
 * GA = Goals against
 * Pts = Points

Key to cup record:
 * En-dash (–) = Adelaide United did not participate or cup not held
 * DNE = The club did not enter cup play
 * QR1 = First qualification round
 * QR2 = Second qualification round, etc.
 * QPO = Play-off qualification round
 * Group = Group stage
 * R1 = First round
 * R2 = Second round, etc.
 * R32 = Round of 32
 * R16 = Round of 16
 * QF = Quarter-finals
 * SF = Semi-finals
 * RU = Runners-up
 * W = Winners