The LCU’s mission is: 

• to support the creative activity of its members by various means;
• to promote their work in Lithuania and beyond;
• to build and strengthen the relations with the world’s musical organisations;
• to participate in Lithuania’s culture and education.

The Lithuanian Composers’ Union was established in Kaunas in 1941 on the initiative of the composer Juozas Gruodis and his associates. In 1948, the Union renewed its activity and held the first congress of the LCU (it was part of the Composers’ Union of the USSR at that time). In 1948–1949, the LCU was chaired by Juozas Talat-Kelpša, and after his death, until 1954, his duties were taken over by the Union’s executive secretary Abelis Klenickis. Subsequent chairs of the LCU were: Stasys Vainiūnas (1954–1962), Eduardas Balsys (1962–1971) and Vytautas Laurušas (1971–1989). 
In 1989, the Lithuanian Composers’ Union was reestablished as an independent organisation. In that year, Julius Andrejevas was elected as the chair of the LCU and held this position until 1991. He was succeeded by Mindaugas Urbaitis (1991–1995), Jurgis Juozapaitis (1996), Gintaras Sodeika (1996–2003), Remigijus Merkelys (2003–2009) and Zita Bružaitė (2009–2017). Currently Mykolas Natalevičius is the chair of the LCU.

In 2005, the Ministry of Culture of the Republic of Lithuania granted the status of an organisation of art creators to the Lithuanian Composers’ Union. All its members have the status of art creator. Currently the LCU includes 115 composers and 72 musicologists. The LCU also has three honorary members: Petras Aglinskas (USA), Hannelore Gerlach (Germany), Raminta Lampsatis (Germany).

The LCU organises:

• Jauna muzika (Young Music) electronic and electroacoustic music festival
• Muzikos ruduo (Music Autumn) chamber music festival in the regions of Lithuania  (in cooperation with the public body Muzikos ruduo)
• Iš arti (Up Close) contemporary music festival in Kaunas (in cooperation with the public body Iš arti)
• Druskomanija international contemporary music festival in Druskininkai and other Lithuanian cities
• Vox juventutis competition of choral works by young composers (in cooperation with the Vilnius Municipality Choir Jauna muzika) 
• Baltic Music Days festival (in cooperation with Latvian and Estonian Composers' Unions)
• Public hearings of composers’ works, solo concerts, presentations of Lithuanian music abroad
• Symposiums and conferences of musicologists (of the Baltic countries – every three years, of Lithuania and Poland – every four years) 

The LCU proposes candidates for state and international awards and honorary titles, state grants and pensions. It publishes books and notes and releases albums.

The LCU is a member of the following organisations:

• Lithuanian Association of Artists
• National Association of Creative and Cultural Industries (KiKa)
• Baltic Contemporary Music Network
• ISCM (International Society for Contemporary Music) 
• IMS (International Musicological Society) 
• ECSA (European Composer and Songwriter Alliance)