Heintje was born the son of a coal miner who had to retire because of silicosis, reducing the family to near poverty. The family opened a small cafe where Heintje used to sing along with the jukebox. When he was 11, he entered a local singing contest. He beat 30 competitors to win the contest. Producer Addy Kleijngeld heard about him and went to audition him at his home. After hearing only a few notes, he took him on as a client and became his manager. Upon becoming wealthy, Heintje moved his family back to his father's birthplace, Neu Moresnet, Kelmis, Liège, Belgium.
He became famous as a child singer, with hit song "Mama" (written by Cesare Andrea Bixio, Bruno Cherubini and Bruno Balz) in 1967, and as a child actor, with his appearances in numerous German films in the 1960s and 1970s (some of these were dubbed into English and also Afrikaans). He enjoyed success with English songs, notable of which is "I'm Your Little Boy". In 1971, The Los Angeles Times described him as, "the hottest property in Europe." The same article quoted the Frankfurter Allgemeine Zeitung as saying of him, "No one is bigger in German show business."
His 1967 recording of "Mama" sold over one million copies, and was awarded a gold record. The following year his debut album Heintje went on to sell over two million copies, resulting in a platinum record award. Other records selling over a million units included "Du sollst nicht weinen", "Heidschi bumbeidschi" and the seasonal album, Weihnachten mit Heintje. His sales in 1968 and 1969 alone totaled over 10 million.
At the age of 20 he also recorded in Afrikaans; his single "Jou Hart Is Weer Myne" reached number 4 on the South African Official Chart in 1975. He was so popular in South Africa that he performed in concert there in the mid 1970s. Heintje also gained great popularity in China in the 1980s. As China introduced its "Gaige Kaifang" policy, his 1970 film Heintje-Einmal wird die Sonne wieder scheinen was among the first wave of movies from the capitalist First World to be imported into China and made available to the general urban population. Heintje-Einmal wird die Sonne wieder scheinen, like most of other foreign films imported into China in the 1980s, received unprecedented popularity among Chinese viewers, with the majority of them having never encountered Western culture before under communist rule. His song "Kleine Kinder Kleine Sorgen" in the movie was so popular that it became an important part of an entire generation of Chinese 80s memory. On two occasions (2010 and 2015), Heintje was invited by Beijing Television as guest performer to sing "Kleine Kinder Kleine Sorgen" on BTV's Chinese New Year Gala.
Heintje continued to sing as an adult, billed as "Hein Simons", and is particularly popular in German-speaking countries. More than 40 million Heintje records have been sold worldwide. He has remained in Neu-Moresnet, Kelmis, Liège, Belgium, his father's birthplace. He was married from 1981 to 2014  and has three children.
- 1967 "Mama"
- 1967 "Oma so lieb"
- 1968 "Du sollst nicht weinen"
- 1968 "Es kann nicht immer nur die Sonne scheinen"
- 1968 "Heidschi Bumbeidschi"
- 1968 "Ich bau' Dir ein Schloß"
- 1969 "Geh' Deinen Weg"
- 1969 "Liebe Sonne, lach doch wieder"
- 1969 "Ich sing' ein Lied für Dich"
- 1970 "Schön sind die Märchen vergangener Zeit"
- 1970 "Deine Tränen sind auch meine"
- 1971 "Schneeglöckchen im Februar"
- 1978 "Und das alles nur weil wir uns lieben"
- 1992 "Ein Mutterherz Soll Niemals Weinen"
- 1994 "Die Heimat darfst Du nie vergessen"
- 1995 "Mama Techno-Version"
- 1998 "Komm, tanz noch mal ganz eng mit mir"
- 2002 "So Wie Ein Stern"
- 2004 "Frauen sind was Wunderbares"
- 1968 Zum Teufel mit der Penne
- 1969 Heintje – ein Herz geht auf Reisen
- 1969 Hurra, die Schule brennt!
- 1970 Heintje – einmal wird die Sonne wieder scheinen
- 1970 Heintje – mein bester Freund
- 1971 Morgen fällt die Schule aus
- 1967 Heintje
- 1968 Weihnachten mit Heintje
- 1969 Ich sing ein Lied für dich
- 1969 Dein schönster Tag
- 1970 Herzlichst Heintje
- 1971 Wenn wir alle Sonntagskinder wär'n
- 1972 Fröhliche Weihnacht überall
- 1973 Ich denk an dich
- 1974 Junger Mann mit 19
- 1978 Ich habe Freunde
- 1989 Herzensmelodie
- 1992 Ich hab' so lange gesucht nach dir
- 1994 Die Heimat darfst Du nie vergessen
- 1996 Mein zweites Leben
- 1998 Ich schenk' Dir meine Liebe
- 1999 Noch einmal mit Gefühl
- 2001 Heute und bisschen gestern – Jubiläumsalbum
- 2002 Rück ein Stückchen näher
- 2003 Von Herz zu Herz by Heintje|Von Herz zu Herz
- 2004 Frauen sind was wunderbares
- 2005 Ich sag' Danke
- 2006 Männer sind einfach zu gut
- 2008 Träum’ mit mir
- 2009 Alles halb so schlimm
- 2011 Leb deinen Traum
- 2014 Thuis
- 2015 Vertrau auf Dein Herz
- 2017 Heintje und Ich
- "Das erste Mal -- Heintje, wie geht es Mama?" (in Dutch). NZZ Folio, The magazine of the Neue Zürcher Zeitung. August 2001. Retrieved 25 July 2015.
- "Europe's Top Singer Faces Crisis at 15" (March 11, 1971) Los Angeles Times
- "Heintje – "Heintje" (1967, LP)". Discogs.com. Retrieved 2013-12-28.
- Murrells, Joseph (1978). The Book of Golden Discs (2nd ed.). London: Barrie and Jenkins Ltd. pp. 222–223. ISBN 0-214-20512-6.
- "小小少年". baike.com. Retrieved 4 June 2015.
- "da music" (in German). Da-music.de. Retrieved 28 December 2013.
- "Heintjes Frau und die Mutter seiner drei Kinder lässt ihn sitzen" [Heintje's wife and mother of his three children leaves him]. BLICK (in German). 28 April 2014. Retrieved 11 December 2017.
- on YouTube
- "Hein Simons: "Weihnachten mit Heintje" als Duett-Album". schlagerplanet.com. Retrieved 13 November 2018.
- "Hein "Heintje" Simons stürmt Schlager-Charts". MDR. February 5, 2019.
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