Leader of the Danish Social Liberal Party from September 2014 to October 2020, he was a member of the Folketing from 2005 to 2021.

[1] He holds a master's degree in political science from the University of Aarhus.

[2] Østergaard was vice-chairman of the party from 2002 to 2005 and has been a member of parliament since the 2005 election.

[2] Following the announcement on 31 August 2014 that Margrethe Vestager is to become Denmark's EU Commissioner, Østergaard was elected leader of the Danish Social Liberal Party and was appointed Deputy Prime Minister of Denmark, as well as Minister of the Interior.

On 7 October 2020 Østergaard resigned as the leader of the Danish Social Liberal Party due to inappropriate sexual behaviour towards fellow Social Liberal MP Lotte Rod.