Pierrepont initially supported President Andrew Johnson's conservative Reconstruction efforts having opposed the Radical Republicans.

In 1871, Pierrepont gained the reputation as a solid reformer, having joined New York's Committee of Seventy that shut down Boss Tweed's corrupt Tammany Hall.

[2] In April 1875, Pierrepont was appointed U.S. Attorney General by President Grant, who, having teamed up with Secretary of Treasury Benjamin Bristow, vigorously prosecuted the notorious Whiskey Ring, a national tax evasion swindle that involved whiskey distillers, brokers, and government officials, including President Grant's private secretary, Orville E. Babcock.

[10] Pierrepont argued that the military trial was suited for Surratt's case and quoted Bible verses that he viewed supported government was created by God for the express purpose of finding the guilty.

[11] Pierrepont argued that because Surratt had assumed an alias name, John Harrison, in staying at a hotel, and had fled the country that this proved his guilt.

[13] From April 25, 1869 to July 20, 1870 Pierrepont served as U.S. Attorney for the Southern District of New York appointed by President Ulysses S. Grant.

[15] Allegations of corruption rapidly grew as rumors spread that Boss Tweed and associates of Tammany Hall were laundering tax payers money in real estate and bribing New York State legislatures for favorable legislation.

[15] New York City workers under the Tammany Hall system were paid excessive rates on the burden of tax payers.

On September 4, at Cooper Union, a large organization of reputed citizens was formed known as the Committee of Seventy, that investigated the corruption of Boss Tweed's Tammany Hall Ring.

By the end of October 1871 the Committee of Seventy had successfully stopped funding Boss Tweed's Tammany Hall by court injunction effectively shutting down the corrupt institution.

On September 25, 1872 reformer Pierrepont gave a speech at the Cooper Union Institute in New York that supported President Grant's reelection.

[18] Pierrepont had observed that southern whites in poverty supported Greeley, while African Americans were loyal to President Grant.

[20] With the prosecution of the Ku Klux Klan by President Grant and Pierrepont's shutting down the Tammany Ring, the general election of 1872 was one of the most fair in United States history.

Saint-Gaudens was so upset over the Pierrepont portrait sculpture that he later stated to a friend, David Armstrong, he would "give anything to get hold of that bust and smash it to atoms".

Pierrepont, a reformer, was teamed up by President Grant with Secretary of Treasury, Benjamin Bristow to rid the government of corruption.

Gen. George H. Williams's Spring, 1873 moratorium of prosecuting civil rights cases and in general was unresponsive to white violent attacks or outrages against African American citizens in the South.

[7] To change his Cabinet coalition, President Grant removed Pierrepont as Attorney General and appointed him minister to Great Britain.

[24] Pierrepont argued citing Gordon v United States that the Postmaster served as in a ministerial position rather than judicial, and therefore Creswell's adjustment was not binding.

[28] After the American Civil War, whiskey distillers in St. Louis developed a tax evasion ring that depleted the U.S. Treasury.

In an effort of reform and to clean up corruption, President Ulysses S. Grant appointed Benjamin Bristow, as U.S. Secretary of Treasury in 1874, who immediately discovered millions of dollars were being depleted from the U.S.

In April 1875, President Grant appointed Pierrepont Attorney General and teamed him up with Bristow to prosecute the Ring and clean up corruption.

[31] Under orders from Grant, Pierrepont controversially sent circular letters to district attorneys in Milwaukee, Chicago, and St. Louis denying immunity to offenders who would testify against the ring.

In March 1876, a rumor spread throughout Washington, D.C., that Attorney General Pierrepont had given information to aid the defense counsel of Orville Babcock in St.

[33] On May 22, 1876 President Grant appointed Pierrepont Minister Plenipotentiary of the United States to Britain, having replaced Robert Schenck, serving until December 1, 1877.

[37] Lord Derby, minister of foreign affairs, told Pierrepont that since Grant had no formal rank in the United States, he had none in Britain.

[37] After his tenure as Minister Plenipotentiary ended, Pierrepont returned to the United States and resumed his private legal practice in New York.

[4] Although Pierrepont was an invalid, for the next two and one-half years he was able to carry on most of his law practice and travel back and forth from his New York residence to his mansion in Garrison.

[4] On Wednesday, March 2, 1892, Pierrepont suffered a massive stroke that paralyzed the right side of his body and he lost the ability to speak.

[4] Pierrepont is primarily known for his success as an attorney appearing for well-known clients in important cases, and for fighting political corruption in federal, state, and city offices.

[31] Although Pierrepont's tenure as Attorney General took place during Reconstruction, his primary interest at the Justice Department was ruling on cases that determined the rights of U.S. citizens abroad.