The dig, directed by Professor Stephen Driscoll of the University of Glasgow and Clyde Archaeology, took place on Saturday at the church during a community fun day.
The ancient site is renowned for the quality of its Viking-age sculpture, but the early medieval carved stone is "quite unlike" any others.
The image on the stone shows a guy standing sideways while toting a round shield and a shaft. The figure can be regarded as a warrior and is likely wielding a sword or spear.
While the warrior's face has suffered significant damage since it was originally carved more than a thousand years ago, amazing features reveal a flowing ponytail and a razor-sharp beard.
Govan Old, the oldest known Christian site in Glasgow, was constructed in 1888 on top of a sacred place that dates back to the sixth century.
Former church pastor Reverend Tom Davidson Kelly referred to it as “possibly the most significant church in Glasgow, including the Cathedral” in 2007.
The Govan Stones museum, which has one of Europe's best collections of early medieval and Viking sculpture, is also located in Govan Old.
Additionally, he asserted that the structure served as a place of worship before Scotland became a country.
Over 30 sculptures from the ancient kingdom of Old Welsh-speaking Britons known as Strathclyde, which ruled the Clyde valley from the fifth to the eleventh centuries AD, are included in the collection.
It contains five hogback monuments that date from the ninth and tenth centuries and are assumed to have served as tomb markers at first.
Even among the outstanding existing collection, which also includes the extraordinary Govan Sarcophagus, the Govan Cross, and five hogback gravestones, a Scandinavian-style funeral monument from the ninth or tenth century, the new discovery, currently dubbed the "Govan Warrior," is exceptional for its quality.