Upon retiring from military life, Hamilton returned to Albany, New York. In January of 1782, Hamilton's wife Betsey gave birth to their first son, Philip. The couple had eight children altogether, two girls and six boys, over the span of twenty years. The couple and their first son lived together in Albany until they moved to Wall Street in New York City in 1883.

In January of 1882, Hamilton petitioned the New York Supreme Court to grant him special waivers so that he could become a lawyer. Ordinarily, would-be lawyers were required to serve a three-year internship before taking the bar exam, but the court granted Hamilton's request because he had served as an aide to George Washington in the army for four years. Hamilton immediately began studying for the upcoming bar exam later that year. His old King's College friend and comrade-in-arms Robert Troup helped him in his studies. To help himself prepare, Hamilton went over old New York court cases and compiled his analysis of the cases in a book called Practical Proceedings in the Supreme Court of New York. Although Hamilton was only a twenty-five-year-old student when he wrote the manual, it became a standard text in New York legal studies for decades afterwards. In October 1882, Hamilton passed the bar exam and was granted the legal right to practice law in the new State of New York.

Hamilton did not begin practicing law right away, however. Instead, he focused his energies on the national financial crises. The fledgling United States faced a plethora of financial hardships. To begin with, war debts had accumulated, and under the Articles of Confederation, which set the guidelines for the government of the United States at the time, Congress did not have the power to forcibly collect taxes from the states to raise money. Some states acknowledged Congress's requests, but others did not, and there were several types of currencies circulating throughout the country. Congress had its own currency, as did some individual states, and even some private banks printed money. Inflation was terribly high as well. In 1781, Hamilton proposed to Robert Morris, Congress's Superintendent of Finance, that a national bank should be created to regulate the new country's money and finances. Hamilton also suggested that Congress be given the power to directly levy taxes. Morris fought for Hamilton's ideas in Congress and appointed Hamilton to the position of Receiver of Continental Taxes in New York in May of 1782. Hamilton accepted, although he thought the position was one of limited possibilities, as he had very little real power to enforce tax collection.

Fortunately for Hamilton, new opportunities arose, and shortly after his appointment as tax collector, Hamilton was elected to Congress as a representative of the State of New York. Hamilton served in Congress for nearly a year, from October of 1782 until August of 1783. During his service, Hamilton participated in the drafting of the peace treaty between the United States and Great Britain that ended the Revolutionary War. Hamilton proposed that naval activity should be banned from the Great Lakes between the United States and British Canada, but his proposals were ignored. Naval power in this region would later prove to be a problem for both countries during the War of 1812.

After eight months as a U.S. Congressman, Hamilton returned to New York in November, 1783, and established a legal practice in his Wall Street home. The practice proved to be very profitable for Hamilton, who represented many of New York's wealthiest businesses and individuals. He also represented many unpopular New Yorkers, including the Tories, who had sided with the British during the Revolution. Many New Yorkers accused Hamilton of betraying his countrymen to profit from wealthy loyalists, but Hamilton responded that the nation should adopt the policy of "forgive and forget." Hamilton felt that any laws designed to punish loyalists would give the United States a bad name and drive loyalist merchants away from the United States when the country most needed their business.

In June, 1784, defended a loyalist in the case of Rutgers v. Waddington, during which he stated that a state "cannot repeal the law of the United States." Hamilton actually lost the case, but the New York City judge concurred that the national government was supreme over the state governments. Hamilton cherished this belief for the rest of his life.