Born in Riverdale, County Tyrone, Ireland, Mulligan immigrated to America at the age of 17 and found work as a stone cutter in Pullman, Illinois, near Chicago.

During the Columbian Exposition in 1893, Taft made Mulligan the foreman of the workshop producing a large amount of sculpture for the exhibition.

[4] Throughout his life, he chaired multiple committees and councils in Chicago with the aim of beautifying the city with affordable works of art.

[5] While most of his career was dedicated to classical sculpture and city beautification projects, he also had a fondness for folk art and often lent his expertise to local artists.

During his time at Bass Lake, Mulligan would work in a number of folk mediums, including local flora.