One of the top dog legal eagles of his day, Pinkney was drawn into politics and diplomacy even though his primary interest was law. Not by choice, mind you: he dipped his toes in the water by becoming a delegate for Maryland's convention to ratify the Constitution, and from there got roped into further involvement by George Washington.
When George Washington offers you a job, you just don't turn the guy down.
Pinkney came from wealthy British Loyalists and attended one of the finest academies in America at the time, King William School. When he graduated, he apprenticed with a physician for a time…probably just because he knew he was smart enough to do pretty much anything.
His law career in Hartford County, Maryland, was a promising start. He distinguished himself with his brains, speechmaking skills, and his insane levels of ambition. This made for an easy-peasy transition into politics. His first elected position was for the Maryland convention to ratify the Constitution, which he opposed.
Despite his minority opinion on the dang Constitution, this did little to slow Pinkney down. He pursued a seat in the House of Representatives, and got accustomed to the spotlight of the House floor. He was famous for being a fop: he wore ridiculous, over-the-top outfits.
In spite of this—or, who know, maybe because of it—Washington appointed Pinkney as one of the representatives of the U.S. in the negotiation of Jay's Treaty of 1794. Here, Pinkney earned his chops as a representative of U.S. interests and a master of maritime law.
Pinkney's return to the States was followed by a series of successful cases that increased the value of his private law practice and his political aspirations: in a move he'd find himself repeating throughout his life, he was appointed Attorney General of Maryland and found he didn't much care for it, and resigned after six months to resume his private practice.
The dude just really enjoyed lawyering, all right? Plus he made a killing at it, so double win for Pinkney.
In his off time, Pinkney offered a sort of guidebook to Baltimore merchants on how to approach the problem of impressment (British vessels essentially going about and abducting Americans to work on their ship), which would convince Thomas Jefferson to appoint Pinkney as an emissary to England.
He worked alongside future president James Monroe in order to secure a treaty over war reparations and the impressment issue, but it didn't go so well: Jefferson had demanded three key concessions and the Pinkney-Monroe dream team failed to deliver any of them. They also took their sweet time in failing, so when they finally did manage to secure the unfavorable treaty it was all a moot point anyway.
In 1807, Monroe was transferred to Spain and Pinkney utilized his new connections to secure Monroe's old job of Foreign Minister to England, which he pretty rapidly began to despise. The British Parliament did not take to kindly to his arrogance, weird clothes, and tendency to steal as much limelight as he possibly could (mostly because it left none for them).
Unlike Rufus King, who was charming the pants off of them, Pinkney was getting sick and tired of British Parliament's obstructionist and haughty attitude towards American legal and political interests.
With the threat of the War of 1812 looming, he returned to the states and washed his hands of the whole idiotic mess. Or so he'd hoped.
Pinkney was appointed Attorney General by Madison upon his return home, but it would be a short-lived thing. The outbreak of war gave Pinkney some interesting ideas about his ability to lead men into battle, despite all evidence to the contrary. He decided to move to D.C. and become a major, hoping to increase his reputation and kill a few of those irritating twits from across the pond while he was at it.
He was wounded rather shortly after his enlistment in the army, and thought that perhaps that was a silly idea in first place and went back to what he knew best: lawyering. He began working for the Maryland Supreme Court, which rapidly got him back into politics again. While he served a term in Congress, his next major post was as foreign diplomat to Russia, of all places. A new, exotic locale was just what Pinkney needed after this rough patch in his career.
He hated it immediately.
He was fortunate in this, however, as relations with Russia quickly became rather obviously untenable. Things were so bad that Pinkney's main order of business was getting as many of these bloody Russians out of the U.S. as possible. The arrest of a certain Russian Consul had soured Russo-American relations somewhat, a souring which would pretty much set the tone for the rest of America's Russian relations. Pinkney dealt with it as quickly as he could and set sail for home and the comforts of his law practice.
But politics weren't quite done with him yet. In 1819 the death of Maryland Senator Alexander Contee Harrison left a vacancy in Maryland politics that Pinkney couldn't resist. He ran for and won the seat in the Senate, and would retain a position in congress until his death three years later.
It was at this time that Pinkney, totally by accident, stumbled into what would later be seen as his primary influence on American law. The issue of slavery was on the rise in America, and with the central debate being in many ways a legal one Pinkney was actually in fairly good spot to make a difference in the issue.
Pinkney, naturally, was a supporter of slavery. Maryland had a long and storied history of slaving, and Pinkney was not about to let his state down. He began to make a series of eloquent speeches before the senate arguing for the rights of the states and slavers in particular. (Ugh.)
He wasn't blatantly biased of course, and when the opportunity arose to resolve the whole mess with the inclusion of a new slave and free state, he jumped at the chance. He was one of the driving forces behind the formation of the Missouri Compromise in the Senate, and was pretty pleased when all the pieces fell into place in (fairly) short order.
Of course, he had missed out on the previous two years of feet-dragging and intense debate…but at least he showed up when it counted.
Even this would not be his most impressive contribution to American law. Despite his position in the Senate, he would go on to make a series of arguments in cases before the Supreme Court that distinguished Pinkney as one of the finest legal minds in American history. He spent so much of his time with his private law practice, it begs the question if he attended any Senate meetings or duties at all.
On the other hand, he was the main hand in the landmark McCulloch v. Maryland and Cohens v. Virginia cases, two of the most important legal precedents in American case law. So maybe his senatorial duties weren't all that important anyhow.
In 1822, in the midst of his closing arguments before the Supreme Court in the case of Richards v. Williams, he collapsed on the Court's floor and was rushed home, where he died forty-eight hours later. It was the perfect end to his career, his flair for the dramatic and his love of the law all rolled up into one.