He studied law and was admitted to the bar in 1760. After a period of practicing law, he became a surveyor in the employ of the
Penn family, and then a
prothonotary and
clerk of the courts of
Northumberland County in the 1770s. During the
American Revolution, he served in the
Continental Army as a commissary. He was also a frequent member of the
Pennsylvania General Assembly in the 1780s. During that period, he was also the Indian commissioner, a judge of the
court of common pleas, and a member of the executive council. After the
ratification of the Constitution Maclay was
elected to the
United States Senate and served in the
1st United States Congress from March 4, 1789, to March 4, 1791. He received a two-year term instead of the usual six-year term for senators after he lost a lottery with the other Pennsylvania senator,
Robert Morris. In the Senate, Maclay was one of the most radical members of the
Anti-Administration faction. He constantly feuded with Vice President
John Adams in the Senate after Adams rejected Maclay's political deal to support his vice-presidential candidacy during the
1789 presidential election. In July 1789 he issued a resolution requiring the
president to request the Senate's permission to dismiss
Cabinet members, but it was defeated by Vice President Adams's tiebreaking vote when Adams convinced
Tristram Dalton and
Richard Bassett to withdraw their support. During Senate debates over the
Residence Act establishing the site of the U.S. permanent
national capital and
seat of government Vice President Adams worked with Morris, who preferred
Philadelphia as the capital, to defeat Maclay's motion placing it near his landholdings on the
Susquehanna River. In his
journal, which is the only diary and one of the most important records of the
First United States Congress, he criticizes Vice President Adams and President
George Washington. He also criticized many of their supporters who ran the Senate and included particular senators, believing that their ways of running the Senate were inefficient. He was unsuccessful in his attempt to be re-elected by the state legislature of Pennsylvania. His diary expresses his dry wit and commitment to democratic principles. Following his retirement from national politics, he was also a member of the
Pennsylvania State House of Representatives in 1795, 1796, and 1797. In addition, he was a
presidential elector in the
1796 presidential election (voting for Jefferson), a county judge from 1801 to 1803, and a member again of the state House of Representatives in 1803. He died in 1804 and was interred in
Old Paxton Church Cemetery in Harrisburg. Several of his relatives were also politicians, including his brother,
Samuel Maclay, and his nephew,
William Plunkett Maclay. ==Mansion and land==