In 1868 he was elected a member of the New York City Board of Education, serving as school commissioner and chairman of the financial committee.
When in 1869 the legislature changed the board from elective to appointive, Lewis was confirmed in his office of school commissioner, and in 1870 was reappointed for a term of five years.
Lewis was one of the founders of the Mount Sinai Hospital, and served, since its organization in 1852, on its board of management as secretary, director, and vice-president, resigning the last-named office in 1873.
He founded (1872) the School-Teachers' Life Assurance Society, and was in 1874 chairman of the relief association for the Ninth Ward.
In 1851, the Ladies' Benevolent Society presented him with a gold medal in acknowledgment of the valuable aid he had rendered that body.