He was the son of Patrick Heron of Kirroughtrie, who had been Member of Parliament for the Stewartry from 1727 to 1741. His mother Margaret was the daughter of John Mackie of Palgoun. He married Jean Home, in 1761, daughter of Henry Home, Lord Kames, but the couple were divorced in 1772.
He was educated at the University of Glasgow.
Heron was elected unopposed at a by-election in March 1795 as the Member of Parliament for the Kirkcudbright Stewartry, filling the vacancy caused by the death of Alexander Stewart. His election was the result of a deal brokered with the support of Henry Dundas whereby he was to alternate the seat with two others However, Heron managed to keep the seat for himself and was re-elected unopposed in 1796.
At the general election in July 1802, he faced a contest from the Tory candidate Montgomery Stewart, son of the Earl of Galloway.
Heron was returned, but Stewart lodged a petition, and on 10 May 1803 the result was overturned in Stewart"s favour by the Committee of the House of Commons which heard the case. The campaigns are recorded in three works by Robert Burns, now known as the Heron Ballads.
Burns was himself a supporter of Heron:
Heron died on 9 June 1803, aged about 68. He was survived by only one child, a daughter Mary.
The following year he succeeded to his father"s baronetcy, becoming Sir John Heron-Maxwell, 4th Baronet.
1st United Kingdom Parliament. 2nd United Kingdom Parliament. 17th Parliament of Great Britain.
18th Parliament of Great Britain]
From 1794 to 1803 he was a Whig Member of Parliament for Kirkcudbright Stewartry.
