Jared graduated from Yale College in 1766, and upon his father's removal to Philadelphia to organize a vice-admiralty court, he was left in charge of the elder Ingersoll's affairs. Later he removed to Philadelphia, where he studied law.
His father, in the midst of the controversies preceding the Revolution, advised him to go to England for the further study of law, and on July 16, 1773, Jared Ingersoll was admitted to the Middle Temple. He went to the Continent in 1776, and two years later he secured passage from Paris to America. He had been admitted to the bar in Philadelphia in 1773.
After his return to America, a friend of the family, Joseph Reed, president of the newly created supreme executive council of Pennsylvania, invited him to look after the interest of Reed's clients at Philadelphia. With this auspicious beginning as a member of the Philadelphia bar, he soon became one of the most distinguished lawyers of the city. He was attorney for Stephen Girard, merchant, and Senator William Blount, against whom impeachment proceedings were brought in 1797.
He was admitted in 1791 to the bar of the Supreme Court of the United States. During the next year he was counsel for Georgia in the case of Chisholm vs. Georgia, the first of a number of cases argued by him involving various phases of federal relations. In opposition to Alexander Hamilton, in 1796 he was an attorney in the first case involving the question of the constitutionality of an act of Congress. He was also counsel in cases connected with foreign relations as affected by constitutional law and the jurisdiction of the courts, notably McIlvaine vs. Coxe's Lessee.
Meanwhile Ingersoll had held many public offices. In 1780 he was elected a member of the Continental Congress and by 1785 he was taking an active part in the agitation for revising or supplanting the Articles of Confederation. He was a delegate to the Federal Convention of 1787, but took little part in its deliberations.
In local politics he was a member of the Philadelphia Common Council in 1789 and from 1798 to 1801 he was city solicitor. From 1790 to 1799 and again from 1811 to 1817 he was attorney general of Pennsylvania; for a short time (1800 - 01) he was United States district attorney for Pennsylvania; and in 1811 he was nominated by Pennsylvania Federalists for the vice-presidency. From March 1821 until his death in 1822 he was presiding judge of the district court for the city and county of Philadelphia.
During his early years Jared abandoned the Loyalist views of his father. He was at first inclined toward democratic views but the events of 1801 seem to have been considered by him "the great subversion, " and thereafter in so far as he took part in politics it was as a Federalist.
Quotes from others about the person
“William Pierce said of him: "Mr. Ingersol speaks well, and comprehends his subject fully. There is a modesty in his character that keeps him back".”
On December 6, 1781, Ingersoll married Elizabeth, daughter of Col. Charles Pettit. Of his three surviving children, one was Charles Jared Ingersoll. Another son, Joseph Reed Ingersoll, well known at the Philadelphia bar, was briefly minister to England in Fillmore's administration.