Robert succeeded to the head of his house upon the death of his cousin, Sir Hector Munro, 2nd Baronet of Foulis who died at just 17 years of age. As the eldest son of Col. John Munro, 2nd of Obsdale, Robert was the head of the Munros of Obsdale family but was also a direct descendant and great grandson of Robert Mor Munro, 15th Baron of Foulis.
As a young man Robert entered the army in 1626 and became an officer in Donald MacKay's regiment, serving first in Danish service and later in Swedish service where he highly distinguished himself during the Thirty Years' War on the continent, particularly during the Battle of Lutzen in 1632. At the time there were three Generals, eight Colonels, five Lieutenant-Colonels, eleven Majors and above thirty Captains, besides a large number of other soldiers all of the name Munro.
On the 26th of August, 1643, during the minority of the former chief, "the Estates of the Kingdom passed an Act for the Committees of War in the shires of Scotland", and among the Commissioners for the Sheriffdom of Sutherland and a par of Inverness-shire, occurs the name of "Sir Robert Munro, tutour of Foulles"; and again on the 24th of July, 1644, in a commission for a similar purpose and for the same Sheriffdom is found the name of "Sir Robert Monro, Tutor of Foullis".
In 1649, the Scottish Parliament separated from the Sherriffdom of Inverness-shire the "lands eastward of Altnalait, Knockravock and the Royal Burgh of Tain", erected the Sherriffdom of Ross, and appointed the Marquiss of Argyll the Sherriff-Principal. Afterwards the commission was granted to Sir Robert Munro, who had been elected Member of Parliament for Inverness-shire in 1649 and for his own County of Ross after it was separated from the County of Inverness, 1649-50, to be Sheriff-Principal of the County of Ross.
In 1651 Robert succeeded to the head of his house, upon the death of his cousin Sir Hector Munro, 2nd Baronet of Foulis who died at just 17 years of age, as already mentioned. Robert took up his residence in Foulis Castle.
In 1654 men of the Clan Chisholm raided lands belonging to Robert Munro, 3rd Baronet of Foulis. Valentine Chisholm and four other "delinquents" plundered 85 cows and 23 horses. Robert wisely pursued the matter through the courts of Oliver Cromwell. Robert Munro of Foulis accused Alexander Chisholm of Comar of allowing his kinsman to carry out the raid.
The court found Robert Munro of Foulis in favour and instructed Alexander Chisholm to produce Valentine Chisholm, who was "known for his barbarity”, and his four followers in court within fifteen days, compensate Foulis and his kinsmen for their losses and also to provide a £ 1,000 bond as security for future good behaviour.
It is worth noting that Robert's younger brother, George Munro, 1st of Newmore was "of different principles" and rose to command the King's forces in Scotland (1674-77).
Robert Munro married before he succeeded as 3rd Baronet of Foulis. He married his cousin Jean Munro, daughter of Hector Munro 1st Baronet of Foulis. They had eight children: