After returning to Washington, Bruff went to work as a draftsman in the office of the supervising architect in the United States Department of the Treasury. In that position, he designed the ornamentation for the south and west wings of the Treasury building in Washington as well as architectural ornamentation for Treasury offices throughout the country. During his tenure in the office, he served under supervising architects Ammi B. Young, Isaiah Rogers, and Alfred B. Mullett. Bruff did not get along with Mullett and left the office in 1869, transferring to the department's registry office. He returned to the Treasury architect's office in 1876 to serve under his friend James G. Hill. By 1887, Bruff was the oldest employee of the United States Government. He remained in his Treasury position until he became ill in early 1889.