In 2021, Alaba signed for Real Madrid; he won the 2021–22 La Liga, Supercopa and Champions League title in his debut season.

He rose through the ranks quickly, and in April 2008 he was named on the first-team substitutes' bench for an Austrian Bundesliga match.

[10] He also played five times for Austria Wien's reserve team,[11] before leaving in summer 2008 to join German side Bayern Munich of the Bundesliga.

In January 2010, it was announced that Alaba would train with the first team for the rest of the 2009–10 season,[16] along with reserve teammates Diego Contento and Mehmet Ekici.

[17] The trio were named on the first-team substitutes' bench for the first time on 10 February 2010, for a DFB-Pokal game against SpVgg Greuther Fürth, and Alaba came on in the 59th minute, replacing Christian Lell.

[18] After one minute on the pitch, and with his second touch of the game, he set up Franck Ribéry to give Bayern a 3–2 lead, in a match they went on to win 6–2.

On 25 April 2012, he played in the 2011–12 UEFA Champions League semi-final second leg against Real Madrid, and scored Bayern's first kick of the shootout as they won 3–1 on penalties.

[24] On 2 April 2013, Alaba scored the seventh-fastest goal (25.02 seconds) in Champions League history to set Bayern on their way to a 2–0 win over Juventus.

[25] On 25 May, he played the full 90 minutes at left-back as Bayern beat Borussia Dortmund 2–1 in the 2013 UEFA Champions League Final.

[35] On 31 March, Alaba suffered a medial ligament damage in his left knee during Austria's 1–1 friendly draw with Bosnia and Herzegovina.

[36] In August 2015 against his former club 1899 Hoffenheim, Alaba's misplaced pass resulted in Kevin Volland scoring in nine seconds, the quickest Bundesliga goal of all time.

On 23 August 2020, he played the full 90 minutes at centre-back as Bayern beat Paris Saint-Germain 1–0 in the 2020 UEFA Champions League Final.

After several attempts to extend his contract, Alaba mentioned that Bayern Munich asked him earlier whether he was interested in a swap deal with Leroy Sané from Manchester City, which he considered as a "slap in the face".

[44] On 28 May 2021, Spanish side Real Madrid announced they had signed Alaba on a five-year contract beginning on 1 July.

[51] During Real Madrid's La Liga match against Villarreal on 17 December 2023, Alaba suffered a torn anterior cruciate ligament in his left knee, requiring surgery and an extended recovery period,[52][53] which lasted about 13 months.

In the poll organised by APA (Austrian press agency) among the coaches of the ten Austrian Bundesliga clubs, Alaba finished top on 21 points, just ahead of Austria Wien's Dutch star Nacer Barazite (20 points) and VfB Stuttgart's Martin Harnik.

[59] He scored a ninth-minute Panenka-style penalty kick on 8 September 2015 to open a 4–1 away win over Sweden at the Friends Arena in Solna.

Although not known to have a fast pace, and his positioning has sometimes been questionable, Alaba possesses a powerful left foot; in which besides his defensive prowess, he is noted for his offensive capabilities and ability to read the game, where he has gained a reputation carrying the ball upfront in attacking plays and supplies his team with passes.