Adelaide United won their first silverware in 2006, when they became premiers of the inaugural A-League season, finishing top of the ladder over Sydney FC by seven points.

Adelaide United formerly held the record for the largest winning margin in an A-League Men match, having defeated North Queensland Fury 8–1 at home on 21 January 2011.

Notable examples include Nestory Irankunda's sale to Bayern Munich for a league record fee, Joe Gauci being bought by Aston Villa, Steven Hall joining Brighton & Hove Albion and Riley McGree signing for Club Brugge, all on transfer fees, as well as facilitating moves overseas for Louis D'Arrigo and Mohamed Toure.

In response, Adelaide United was created on 12 September 2003, with real estate businessman Gordon Pickard funding the new club and former Soccer Australia and FIFA executive Basil Scarsella as chairman.

After a successfulhome-and-away season, including an unbeaten seven-match streak during November and December 2003, Adelaide United reached the NSL preliminary final, ultimately losing to Perth Glory.

The governing body, Australian Soccer Association (later Football Federation Australia), shut down the league in preparation for the launch of the fully professional A-League almost 12 months later, on 26 August 2005.

The club focused on bringing several Adelaide-born players back to South Australia, such as Angelo Costanzo, Travis Dodd, and Lucas Pantelis, who had previously played for Adelaide City SC in the NSL.

Adelaide United started the season well by winning the A-League Pre-Season Challenge Cup, beating reigning champions Central Coast Mariners 5–4 on penalties after 1–1 at the end of extra time.

Coach John Kosmina was sacked the following wee owing to the poor performance at the grand final as well as for alleged abuse of two Channel 10 reporters.

Adelaide United participated in the 2008 AFC Champions League after finishing runner-up in the 2006–07 regular season and finals series to Melbourne Victory.

The Reds defeated Waitakere 2–1 via two set plays from Paul Reid to secure a rematch with ACL rivals Gamba Osaka on 14 December – the third meeting between the two sides in three weeks.

[16] The Reds fought valiantly and created many opportunities, in particular Travis Dodd,[17] but lost 0–1 after a 23rd minute shot by Gamba midfielder, Yasuhito Endō.

[21] Regardless of this situation, the FFA ensured that Adelaide would have the funds available to recruit in the off-season and to maintain the club, whilst they would negotiate the new ownership deals.

[22] Adelaide were drawn into Group H alongside 2009 Asian Champions Pohang Steelers, Chinese sister club Shandong Luneng and Sanfrecce Hiroshima.

Following 18 months under Football Federation Australia (FFA) financial administration, it was announced on 8 November 2010 that a South Australian consortium had taken over ownership of the club with a ten-year licence.

Off-season transfers marked the departure of Captain Travis Dodd, long-serving players Lucas Pantelis and Robert Cornthwaite, and of fan favourites Mathew Leckie and Marcos Flores to overseas clubs.

[29] As part of Kosmina's takeover of the head coaching position, Eugene Galeković was named club captain on 28 December 2011, replacing Jon McKain.

[30] Their fourth appearance in the competition – more times than any other Australian club – Adelaide qualified for the 2012 AFC Champions League playoff round by finishing third in the 2010–11 A-League.

Carrying over from the previous season, Josep Gombau was quick to implement a possession-based football style at Adelaide, all the way from the grassroots level of local soccer to the senior side.

[44] During these seasons, Adelaide placed a large emphasis on bringing through young players from South Australia, and their NPL squad, notable examples during this period were Joe Gauci, who has since earned a cap for the national team,[45] Bernardo, Mohamed Toure, Yaya Dukuly, Ethan Alagich, Asad Kasumovic, Jonny Yull and Nestory Irankunda.

Craig Goodwin, who had recently scored against France and Argentina in the 2022 World Cup, won the 2023 Johnny Warren Medal but returned to Al-Wehda FC in the winter of that year.

Adelaide's 2023–24 season began with massive success, beating the reigning Champions Central Coast Mariners and the Premiers Melbourne City with a combined score of 9–0.

Highlights of these opening games include Joe Gauci's penalty save against Jamie Maclaren, a free kick goal from 17-year-old Nestory Irankunda, and a brace off the bench from Bernardo.

[47] On 14 November 2023, Adelaide United confirmed that they had agreed terms with Bayern Munich for the sale of 17-year-old winger, Nestory Irankunda,[48][49] to join the club at the end of the season.

[60][61] The second half of the season saw United drop towards the bottom of the ladder, going winless for seven consecutive matches, breaking their streak with a 1–0 win away to Newcastle Jets,[62] and a first home win in three months against Western United thanks to a Nestory Irankunda hat-trick, who became the youngest hat-trick scorer in A-League history, and the second youngest in Australian national league history.

In February 2009 the club's head coach, Aurelio Vidmar referred to the City of Adelaide as a "Pissant Town" after suffering a heartbreaking loss.

[86] The record attendance for Hindmarsh Stadium was a full house of 17,000 on 12 November 2008 against Gamba Osaka in the historic second leg of the ACL final.

[110] Qingdao Red Lions are owned by former chairman Piet van der Pol, with the partnership being forged following his acquisition of Adelaide United in 2018.

[111] Then Director of Football Bruce Djite said, "The idea is to develop Chinese players to create stronger links between us and Qingdao Red Lions.

Adelaide United's record home attendance of all competitions at Hindmarsh Stadium was 17,000 against Gamba Osaka in the AFC Champions League Final in 2008.