Oskar Carl Gross was born in Vienna, Austria on November 29, 1871, the son of Rudolf and Jeanette Kurzweil Gross. His father was a distinguished architect and engineer. After graduating from the Viennese Polytechnic he entered the Imperial Academy of Fine Arts in Vienna, though his father wanted him to follow in his footsteps and become an architect. He was one of 32 individuals accepted out of 300 that had applied. The extremely talented Oskar had made such progress at the Academy that his professors had given him the free use of a studio including expenses. His professors also sent portrait commissions to him and upon leaving the Academy in 1897 he had earned $1500 as a student. But now as an independent artist his former teachers discontinued their assistance and commissions were hard to obtain.

In 1898 he entered and won a competition to display two of his murals in the Austro-Hungarian State Buildings at the 1900 World's Fair in Paris. It was at the Paris World's Fair that his work was seen by Louis Sullivan and Daniel H. Burnham. Burnham invited him to come to the United States to provide decorations for some of his buildings and in May of 1902 he settled in Chicago. His home and studio was located at 19 East Pearson Street, the building that would also later house the office of architect Thomas Eddy Tallmadge. Through his connections with Burnham he was soon in demand as a muralist throughout the country and from 1902 until 1912 he painted murals in many Chicago buildings and elsewhere. Some of the last murals that he painted were titled "Cows in the Field" and "Farming Scene" for Louis Sullivan’s 1912 masterpiece, Owatonna Bank, in Owatonna, Minnesota.

Gross began to give up painting murals and concentrated on portrait, figure painting and etchings. In 1911 he showed his paintings in an exhibition at the Art Institute of Chicago. This marked a return to the type of painting that he enjoyed the most, His paintings won him numerous awards throughout the years and he traveled about the United States painting portraits but always preferred to paint in his Pearson Street studio. From 1926 thru 1932 he also taught portrait painting at the Chicago Academy of Fine Arts. One of his best known works was a portrait of General Douglas MacArthur, which was commissioned by the Chicago Tribune. Other famous persons that have been known to sit for Gross include Louis Sullivan’s partner Dankmar Adler and Amos Alonzo Stagg, famous University of Chicago football coach.

Gross belonged to many groups including the Arts Club of Chicago, the Chicago Galleries Association, the Palette and Chisel Academy of Fine Arts, Cliff Dwellers and the Chicago Painters and Sculptors. He died at age 91 on August 19, 1963. He was cremated and his ashes were scattered over the Children's Garden at Lincoln Park in Chicago, a place that he used to enjoy spending time at.