His parents were Johan François Hendrik Jacob Ernestus Mackay, a member of the Provincial Council of Gelderland and the brother of the 10th Lord Reay, and his wife Margaretha Clara Françoise van Lynden.

At the age of six, he was among the first 116 students of De Klokkenberg, the first particular school in the area, which was established primarily at the hands of his father, despite enduring opposition from the municipal and provincial governments.

He left University on 27 November 1862 after defending his dissertation "The exclusion of clergy and ministers of Religion in the Legislature in accordance with art.

On 4 April 1876, he was elected as a member of the House of Representatives for Amersfoort, defeating the liberal Willem Hendrik de Beaufort.

[2][3] Two years later, after the right won a parliamentary majority in the 1888 general election, Mackay was appointed as formateur, tasked with composing a cabinet.

In 1890, after his budget failed to pass through the Senate, Levinus Wilhelmus Christiaan Keuchenius resigned, and Mackay succeeded him as Minister of Colonial Affairs.

A year later, a bill regarding military organisation failed to pass through the House, opposed by many Catholics, and the cabinet resigned on 21 Augustus 1891.

After this constitutional amendment caused some Anti-Revolutionaries to split off and found the Christian Historical Union, Mackay left some ambiguity over his alignment.