Walter Lewis spent his early years in the Missouri area, obtained a degree from William Jewell College, and then went on to Louisville, Kentucky, attending Southern Baptist Theological Seminary. He later earned his Ph.D. by attending various schools in Germany. He was on the faculty of William Jewell College from 1910-1922, with the exception of his service as a U. S. Army Chaplain during W.W.I in France.

He was appointed as a special representative of the American Baptist Foreign Mission Society to Europe. He helped administer American government relief in Russia when famine hit that country in the winter of 1922-1923. He was later asked to take a second journey to Russia that winter, where he administered the distribution of clothing sent by the Baptists of America. His position served as liaison between national Baptist leaders in Europe and the American Baptist Foreign Mission Society in the US.

In 1939 he became General Secretary of the Baptist World Alliance in London, with the particular responsibility of post-war relief, serving until 1947. During W.W.II he shuttled across the Atlantic several times in a successful effort to preserve Baptist communication channels. In 1948, Dr. Lewis was instrumental in moving the headquarters of the Baptist World Alliance to Washington, DC. Although he was then 70 years old, he continued to serve that organization for five more years, directing Baptist relief work across war-ravaged Europe. He passed away after a fulfilling life, perhaps better known in Europe than in his native America. He is buried in Arlington National Cemetery.