Matti Oskar Helenius-Seppälä (27 June 1870, Pälkäne – 18 October 1920) was a Finnish social scientist, temperance movement activist and politician. He was a member of the Parliament of Finland from 1908 to 1909, from 1911 to 1914, in 1917 and from 1919 to 1920, representing the Christian Workers' Union of Finland (SKrTL). He was married to the temperance activist and social worker, Alli Trygg-Helenius.^[1]

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He is buried in the Hietaniemi Cemetery in Helsinki.^[2]