Gade was born in Copenhagen, the son of a joiner and instrument maker. He began his career as a violinist with the Royal Danish Orchestra, which premiered his concert overture Efterklange af Ossian ("Echoes of Ossian") in 1841. When his first symphony was turned down for performance in Copenhagen, he sent it to Felix Mendelssohn. Mendelssohn received the work positively, and conducted it in Leipzig in March 1843, to enthusiastic public reaction. Supported by a Danish government fellowship, Gade moved to Leipzig, teaching at the Conservatory there, working as an assistant conductor of the Gewandhaus Orchestra, and befriending Mendelssohn, who had an important influence on his music. In 1845 he conducted the premiere of Mendelssohn's Violin Concerto in E minor. He also became friends with Robert Schumann and Robert Franz.
At Mendelssohn’s death in 1847, Gade was appointed to his position as chief conductor but was forced to return to Copenhagen in the spring of 1848 when war broke out between Prussia and Denmark. In Copenhagen Gade became acquainted with the composer Cornelius Gurlitt and they remained friends until the latter's death. Gade became director of the Copenhagen Musical Society (Musikforeningen), a post he retained until his death. He established a new orchestra and chorus, while settling into a career as Denmark's most prominent musician. Under his direction, the Music Society reached its peak. He also worked as an organist; though he lost the prestigious position of organist at Our Lady, today's Copenhagen Cathedral, to Johan Peter Emilius Hartmann, he served in the Church of Holmen in Copenhagen from 1850 until his death. Gade was joint director of the Copenhagen Conservatory with Hartmann (whose daughter he married in 1852) and Holger Simon Paulli. An important influence on a number of Scandinavian composers, he encouraged and taught Edvard Grieg, Carl Nielsen, Elfrida Andrée, Otto Malling, August Winding and Asger Hamerik. 
Among Gade's works are eight symphonies, a violin concerto, chamber music, organ and piano pieces and a number of large-scale cantatas, Comala (1846) and Elverskud (1853) among them, which he called "concert pieces" (koncertstykker). These products, embraced post-1848 as works of Romantic nationalism, are sometimes based on Danish folklore. Apparently Gade never rated "The Bridal Waltz" (Brudevalsen). It was rescued by August Bournonville in his ballet A Folk Tale (Et folkesagn) and became an essential part of Danish weddings.
- "Gade, Niels Wilhelm". Salmonsens konversationsleksikon. Retrieved January 1, 2020.
- Robert Franz's 12 Gesange Op. 4 (1845) is dedicated to "My friend Niels W Gade".
- "Cornelius Gurlitt". Deutsche Digitale Bibliothek. Retrieved January 1, 2020.
- Niels Bo Foltmann. "Niels W. Gade". Den Store Danske, Gyldendal. Retrieved January 1, 2020.
- See Anna Celenza's The Early Works of Niels W. Gade, especially Part Three, for more about the sources of Gade's programs and their connection to Danish nationalism.
- "August Bournonville". The Kennedy Center. Retrieved January 1, 2020.
- "A Folk Tale (1854)". bournonville.com. Retrieved January 1, 2020.
- "Hartmann, Johan Peter Emilius, 1805-1900". Dansk biografisk Lexikon. Retrieved January 1, 2020.
- Celenza, Anna Harwell. The Early Works of Niels W. Gade: In Search of the Poetic. Aldershot: Ashgate, 2001.
- Lee, Justin. Niels Gade at the Wayback Machine (archived December 5, 2008) Programme notes
- Wasserloos, Yvonne: Kulturgezeiten. Niels W. Gade und C.F.E. Horneman in Leipzig und Kopenhagen. Hildesheim, Zürich und New York 2004.
- Wasserloos, Yvonne: „Formel hält uns nicht gebunden, unsre Kunst heißt Poesie“. Niels W. Gade und Robert Schumann – Übergänge zwischen Poetischem und Nationalem, in: Henriette Herwig/Volker Kalisch/Bernd Kortländer/Joseph A. Kruse/Bernd Witte (Hg.): Übergänge. Zwischen Künsten und Kulturen. Internationaler Kongress zum 150. Todesjahr von Heinrich Heine und Robert Schumann. Stuttgart u. Weimar 2007, S. 521–540.
- Wasserloos, Yvonne: “Hearing through eyes, seeing through ears.“ Nation and landscapes in the works of Niels W. Gade, Edvard Grieg and Carl Nielsen, in: Studia Musicologica Norvegica 33 (2007), S. 42–52. http://www.griegsociety.org/filer/1139.pdf
|Wikisource has the text of the 1911 Encyclopædia Britannica article Gade, Niels Wilhelm.|
- Free scores by Niels Gade at the International Music Score Library Project (IMSLP)
- Free scores by Niels Gade in the Choral Public Domain Library (ChoralWiki)
- Niels Gade: Novelletten for Piano Trio, Op.29 sound-bites
- Octet in F major, op. 17 (parts) From Sibley Music Library Digital Scores Collection
- 3 Tonstuecke for Organ, op. 22 From Sibley Music Library Digital Scores Collection