He attended secondary school in Vaduz and conducted an apprenticeship as a bricklayer.
He attended federal trade school in Innsbruck and then worked as a master bricklayer.
[1] He was the first Landtag member to actively support the introduction of women's suffrage in Liechtenstein, starting from 1965.
[1][3] Additionally, he was also a member of the Vaduz municipal council from 1969 to 1972 and again from 1975 to 1983.
[1] Gassner married Ursula Spörry on 18 October 1956 and they had two children together.