He returned to New York City in 1889. He was a member of the New York State Assembly (Kings Co., 18th D.) in 1896. He served as commissioner of records of Kings County, New York from 1899 to 1904. He served as delegate to the Republican National Convention in 1900.
Waldo was elected as a Republican to the Fifty-ninth and Sixtieth Congresses (March 4, 1905 – March 3, 1909). He was not a candidate for renomination in 1908. He resumed the practice of law in New York City. He moved to Los Angeles, California, in 1913, to Pasadena, California, in 1918, and continued the practice of his profession. He died in Pasadena, California on June 16, 1942. He remains were cremated and the ashes deposited in the New Cemetery, Scotland, Connecticut.