Robert was born c.1525, third son of Sir Lawrence Mercer of Meikleour and Janet Dundas.
He matriculated at St Andrews on 11 December 1531 (as a child).
He was exhorter and parson of Banchory-Devenick, Aberdeenshire in 1567 (admitted before 1574).
In the Assembly in 1576, a complaint was made against the Superintendent of Angus and Mearns anent his admission, who replied that he had been admitted with the advice of the brethren of Aberdeen, by whom he had been tried.
He married Catherine Blair, probably in 1544.
He died before 25 February 1578 when his son of the same name succeeded him in the parish.
- Malcolm Mercer (b:c.1545-50. Rector of Crieff. d:after 1594)
- Robert Mercer (b:c.1550-5. d:between 1618 and 1622)
- Thomas Mercer (b:c.1550-5)