Born near Osceola Mills, Centre County, Pennsylvania, to Welsh immigrants,[1] Lewis worked in the local coal mines from 1878 to 1892.

[2][3] Lewis served as a member of the Maryland State Senate from 1902 to 1906,[2][3] and was an unsuccessful Democratic candidate for election to the Sixty-first Congress in 1908.

[2] He was again an unsuccessful candidate for the Democratic nomination for the United States Senate in 1922, and resumed the practice of law in Cumberland.

[2] He was again elected to the Seventy-second and to the three succeeding Congresses, serving the sixth district of Maryland from March 4, 1931, to January 3, 1939, but was not a candidate for renomination in 1938, having run for senator, challenging incumbent Millard Tydings in the Democratic primary.

[3] David John Lewis was the leading expert on social insurance legislation on the House Ways & Means Committee.