He met his longstanding partner Chester Holmes Aldrich when they worked together at the office of Carrère and Hastings in the years before the turn of the 20th century. They formed their partnership after Delano's return from Europe in 1903 and almost immediately won commissions from the Rockefeller family, among others. Delano & Aldrich tended to adapt conservative Georgian and Federal architectural styles for their townhouses, churches, schools, and a spate of social clubs for the Astors, Vanderbilts, and the Whitneys. Separately (Delano was the more prolific) and in tandem they designed a number of buildings at Yale. Delano taught at Columbia University from 1903 to 1910.