Bettel was born on 3 March 1973 in Luxembourg City. His father, Claude Bettel, was a wine merchant and his mother, Aniela, French of Russian descent, grandniece of famous composer Sergei Rachmaninoff. After finishing the European School, Bettel obtained a master's degree in Public and European Law and a DEA in Political Science and Public Law from Nancy 2 University in Nancy, France. He also studied maritime law as well as canon law at Aristotle University in Thessaloniki, Greece. He participated in the Erasmus Programme. For four years in the early 2000s he hosted Sonndes em 8, a weekly talkshow, on the now-defunct private T.TV television network.
In the 1999 communal elections, Bettel was elected to Luxembourg City's communal council, finishing sixth on the DP's list. On 12 July 2001, he qualified as a lawyer. By the time of the 2004 legislative election, Bettel had significantly consolidated his position, and finished fourth (of the five DP members elected), giving him a seat in the Chamber of Deputies. On 28 November 2005, after the communal elections in which he was placed fourth on the DP list, Bettel was appointed échevin in the Council of Luxembourg City.
Following municipal elections on 9 October 2011, at the young age of 38, Bettel was sworn in as Mayor of Luxembourg on 24 November 2011.
Bettel ran for the Chamber of Deputies in the 1999 legislative election, and finished 10th amongst DP candidates in the Centre constituency, with the top seven being elected. However, the DP overtook the Luxembourg Socialist Workers' Party (LSAP) as the second-largest party, and its members formed the majority of the new government as the Christian Social People's Party's (CSV) coalition partners. Thus, with Lydie Polfer and Anne Brasseur vacating their seats to take roles in the government, and Colette Flesch not taking her seat so as to focus on her role as Member of the European Parliament, Bettel was appointed to the Chamber, starting 12 August 1999.
In 2013, Bettel was elected leader of the Democratic Party, and in the 2013 election, led the party to a third-ranked position in parliamentary seats. On 25 October, Bettel was designated by Grand Duke Henri as the formateur for the next government. He assumed his post as Luxembourg's Prime Minister on 4 December 2013. In the government's coalition of the Democratic Party, Luxembourg Socialist Workers' Party and The Greens, he also holds the functions of Minister of State, Minister for Communications and the Media, and Minister of Worship.
His policies were expected to include reforms on same-sex marriage, replace religious instruction in schools with general ethics classes and cut spending to maintain Luxembourg's AAA credit rating.
Bettel is openly gay, and has stated that increasingly in Luxembourg "people do not consider the fact of whether someone is gay or not". Bettel is Luxembourg's first openly gay Prime Minister and, worldwide, the third openly gay head of government following Iceland's Prime Minister Jóhanna Sigurðardóttir (2009–2013) and Belgium's Prime Minister Elio Di Rupo (2011–2014). As of June 2017, he is one of three openly gay world leaders in office, the others being Leo Varadkar, the prime minister of Ireland; and Ana Brnabić, the Prime Minister of Serbia.
Bettel has been in a partnership with Gauthier Destenay since March 2010. In August 2014 Destenay proposed to Bettel, who accepted. Bettel and Destenay married on 15 May 2015; same-sex marriage law reforms had come into effect on 1 January 2015, after passing in June 2014.