[3] Soper received a recess appointment from President Herbert Hoover on May 6, 1931, to a seat on the United States Court of Appeals for the Fourth Circuit vacated by Judge Edmund Waddill Jr.

With Chief Judge Charles Sterling Hutcheson of the Eastern District of Virginia and new Eastern District judge Walter E. Hoffman, Soper heard many desegregation cases arising from the Byrd Organization's declared policy of Massive Resistance to racial desegregation.

His last judicial act (as a senior judge) was an order allowing an African American, Henry Gantt, to attend the school of architecture at Clemson University.

[4] Attorney General Robert F. Kennedy and Maryland Governor Theodore McKeldin were among the pall bearers at his funeral.

[citation needed] Soper's papers were donated to the Maryland Historical Society Library with a 25-year restriction on access, which with a snafu meant archiving did not begin for decades.