He began is career at Saskatchewan Rapid Wien in 1911 and from 1913 to 1920 was on the club"s first squad. During the waning years of the Austro-Hungarian Empire Rupec played ten matches for the Austrian national team In 1920 he joined a top Croatian side HŠK Građanski Zagreb.
He played with the club until the end of his career in 1928.
He later coached HAŠK Zagreb to the national championship in 1938. Rupec was part of the Kingdom"s first national team, and had 9 caps.
He died in the summer of 1983 at the age of 87 in Zagreb.