Thom Denijs, born Thomas Johannes Denijs, was a Dutch singer with a baritone/bass range and a specialist in oratorio. He was born into the family of cashier Johannes Denijs and Margaretha van der Haagen. His grandfather conducted the Langedijk Singing Society; his father was a bass, his sister Lenamie Denijs was a violinist, and his brother Simon Denijs was also a baritone/bass.
Denijs studied at the Amsterdam Conservatory with Cornélie van Zanten and Johannes Messchaert. His general studies there included instruction from Daniël de Lange, Bernard Zweers and Jean Baptiste Charles de Pauw. After receiving an allowance from Queen Wilhelmina, he continued his studies in Berlin and also studied in Paris with Jules Algier.
From 1901 to 1903 he belonged to the Amsterdam Lyric Theatre. There he sang Papageno in Die Zauberflöte alongside his future wife, the singer and pianist Emmy Kruijt, who performed Papagena. He continued to sing opera roles until 1905, then concentrated more strongly on oratorio work.
Denijs taught singing at the Rotterdam Conservatory from 1903 to 1910, but resigned because of his busy career in the Netherlands and abroad. He gave concerts in the Netherlands, Belgium, France, Germany and Austria-Hungary. He settled in Berlin in 1911, but the First World War brought him to The Hague. In 1925 he gave several masterclasses in Bern, and in 1926 he travelled to the United States for concerts conducted by Willem Mengelberg.
Between 1902 and 1935, Denijs appeared at least 174 times with the Concertgebouw Orchestra. Usually under Mengelberg's direction, he sang the baritone role in Johann Sebastian Bach's St Matthew Passion, as well as appearing in Ludwig van Beethoven's Symphony No. 9. Some of his recordings survive, at times with piano accompaniment by his wife; several songs were included on the Philips Records compact disc The Best of Sweet Voices.
Queen Wilhelmina appointed Denijs to the Order of Orange-Nassau in 1927. He died from complications following an operation at Bronovo Hospital and was buried at Nieuw Eykenduynen. A sculpture by Corinne Franzén-Heslenfeld was unveiled on his grave in 1936.