Before Mr. Boutwell was admitted to the bar he was retained by the county commissioners of Middlesex County to appear before a legislative committee of the years 1854 and 1855 against the division of that county and the erection of a new county to be called the county of Webster with Fitchburg for the shire. Emory Washburn appeared for Worcester County and Rufus Choate for Fitchburg and the new county. The application failed in 1855 and again in 1856. Mr. Boutwell's arguments on this petition, made March 25, 1855, and April 23, 1856, were remarkable for power and eloquence, and largely influenced the final result. From 1862 to 1869 he was retained in many causes, the most important of which was the controversy over the contract between the commonwealth and Gen. Herman Haupt for the construction of the Hoosac Tunnel. The hearing before a legislative committee occupied about twenty days and ended in the annulment of the contract. For several years Mr. Boutwell was associated in Boston with J. Q. A. Griffin. Afterward he was in partnership with Henry F. French until 1869, when he became Secretary of the Treasury in the Cabinet of President Grant. He filled this position with great ability for four years, originating and promulgating, among other measures, the plan of refunding the public debt. During that period he made but one argument, when he appeared in the Supreme Court on the appeal by his client of a patent case, of which he had had charge from the beginning. From 1863 to 1869 he had been a member of the 38th, 39th, 40th and 41st Congresses, serving on the committees on the judiciary and on reconstruction, and being chairman for a time of the latter body. While representing his district in Congress Mr. Boutwell gained considerable experience in the proceedings against President Andrew Johnson, who was impeached for high crimes and misdemeanors, and he was selected as one of the managers on the part of the House. In a remarkably brilliant speech before the House on December 5 and 6, 1867, he maintained the doctrine that the president and all other civil officers could be impeached for acts that were not indictable, although the contrary was held by many eminent lawyers, including President Dwight, of Columbia College, who wrote a treatise in support of his theory. But the House preferred articles that did not allege an indictable offence and the Senate sustained them by a vote of thirty-five to eighteen, one less than the number necessary for conviction. On April 22 and 23, 1868, Mr. Boutwell, on behalf of the managers, addressed the Senate, delivering one of the strongest and ablest arguments on record, and thus completing, as a lawyer, the most exhaustive labor he ever attempted. He was a member of the Committee of Fifteen which reported the Fourteenth Amendment, and while serving on the committee on the judiciary he reported and carried through the House the Fifteenth Amendment to the Constitution of the United States.