Merkatz was born on 17 November 1930 in Wiener Neustadt, the son of a toolmaker.

After World War II he was an active Boy Scout in Wiener Neustadt.

Then he found employment in theatres, most notably in Munich, Salzburg, Hamburg and Vienna (Theater in der Josefstadt).

In the role of Edmund Sackbauer (Mundl) in the 1970s, he became famous as the typical Viennese (Ein echter Wiener geht nicht unter).

From 1999, Merkatz was chairman of the human rights group SOS Mitmensch.