The minority Country Party was largely Ulster-Scot, centered in New Castle County, and quickly advocated the idea of independence from the British.

However, his Ulster-Scots background and prominence in the Presbyterian Church community made him acceptable to many who normally associated themselves with the Country Party.

McKinly was elected Sheriff of New Castle County in 1757, served 4 three-year terms as Chief Burgess of the town of Wilmington between 1758 and 1776.

In the events leading up to the American Revolution, he became a member of the Delaware Committee of Correspondence in October 1773, and was chairman by November 1774.

On February 12, 1777, the General Assembly elected him to be Delaware's first Chief Magistrate or President and he served until he was replaced on September 22, 1777.

The evening after the battle the 71st Regiment, Frazer's Highlanders, were sent the 10 miles to Wilmington to meet up with the British fleet on the Delaware River and establish a hospital for the wounded.

They took the President from his bed at dead of night, and seizing a sloop that lay in the stream, loaded it with valuables stolen from the people, a large quantity of public and private money, many of the public and private records and all the papers and certificates of the loan and treasury offices.

[3]In an August 20, 1778 letter to Henry Laurens, the President of the Continental Congress, McKinly wrote: Several circumstance concurred to render my staying at Wilmington necessary to the public whilst the enemy were moving toward Philadelphia, and being more solicitous to perform my duty, than for my own personal safety, I was unexpectedly made a prisoner in my own house there on the night succeeding the 12th day of September last, by the 71st British Regiment, said to contain at that time of 900 men, who were detached to take possession of that place for the accommodation of such of their Army as were wounded the day preceding, at the Battle of Brandywine.

[citation needed] After his release, McKinly returned to his medical practice and remained active in Wilmington affairs.

He never held political office again, refusing an appointment to the Continental Congress and losing a General Assembly election for his old job as president in February 1783.

There is a marker placed in his memory in the cemetery at South Park Drive, near its intersection with North Adams Street.

Although he was an Ulster-Scot native, and resident in New Castle County, he was a moderate on the issue of independence, viewing the break with Britain with reluctance and regret.