He played football professionally for his hometown club Red Star Belgrade and FK Napredak Kruševac in Serbia, Bonnyrigg White Eagles Football Club (under the name of Sasha Jankovic) in Australia, AS Cherbourg Football and Pau FC in France, and Kansas City Wizards in the United States, before ending his playing career aged 28, due to a knee injury.
While playing at Pau FC, Janković met his compatriot, coach Slavoljub Muslin who would turn out to be an important figure for his eventual venture into coaching. Following the injury that forced him to end his playing career, Janković came into the Red Star organization (club coached by Muslin at the time) in an adviser-scout role during the early 2000. At the end of the 2000–01 season that saw Red Star win another league title (after winning the league and cup double the previous season), Ratko Dostanić, Muslin's assistant, took the head coaching job at FK Obilić, and Muslin offered the vacated place to Janković who thus became Red Star's assistant coach on July 5, 2001 at the age of 29.
However, Janković wouldn't get to stay at his new job for long as very early into the 2001–02 season Muslin abruptly resigned as head coach after the 2001–02 UEFA Champions League qualifying first leg loss to Bayer Leverkusen and Janković left as well.
In March 2002, Muslin resurfaced as head coach at Levski Sofia and Janković followed him there to be his assistant. In April 2003, Muslin got the sack and Janković left again as well.
Couple of months later, during summer 2003 offseason, the duo returned to their old stomping grounds at Red Star. After Zoran Filipović got sacked, Muslin got the head coaching job, and, Janković, by now his established second-in-command, was on his way to Belgrade as well.
From there Janković followed Muslin to Metalurh Donetsk, Lokeren, Lokomotiv Moscow, and back to Lokeren, respectively.
From July 2007, he has been an advance scout in Red Star, and his duties mainly included scouting opponents' players and tactics.
After Milorad Kosanović's resignation on 9 November 2007, Janković was appointed new head coach of Red Star. Yet, after failing to earn a title in the national championship or in the national cup, he was fired June 11, 2008, to be replaced by Zdeněk Zeman.
Janković has since been appointed head of the Red Star Belgrade Football School.
On April 6, 2009 he has been named the new SC Lokeren coach, the Serbian signed until June 2010 and replaces Georges Leekens. On 25 October 2009 Janković was fired after a series of bad results.
Aleksandar is married and has two children. His father is a notable Serbian sports journalist Dobrivoje "Bobi" Janković. He has been dubbed as "Serbian Mourinho" due to his charisma and cult status he has enjoyed among the players and fans.