Thayer was a commissioner to revise the revenue laws of Pennsylvania in 1862.
Congress He was elected as a Republican to the
Thirty-eighth and
Thirty-ninth Congresses, during which he served on the committee on the bankrupt law and was the chairman of the
United States House Committee on Private Land Claims. He declined to be a candidate for re-election in
1866, and resumed the practice of law. While in Congress, Thayer criticized the use of portraits of living persons on US currency, suggesting that the Treasury's privilege of portrait selection for currency was being abused. Spearheaded by Thayer, on April 7, 1866 Congress enacted legislation specifically stating "that no portrait or likeness of any living person hereafter engraved, shall be placed upon any of the bonds, securities, notes, fractional or postal currency of the United States."
Later career Thayer was judge of the district court of Philadelphia from 1867 to 1874, and served as president judge of the court of common pleas of Philadelphia from 1874 until his resignation in 1896. In 1873 he was appointed on the board of visitors to
West Point, and wrote the report. (Some 40 years earlier, his cousin
Sylvanus Thayer had been superintendent of West Point.) He was elected as a member to the
American Philosophical Society in 1877. He was elected by the judges of the common pleas court prothonotary of Philadelphia in 1896. He also engaged in literary pursuits. == Death and burial ==