He fought with the Jacobite side under Viscount Dundee at the Battle of Killicrankie Pass in 1689, where General Hugh MacKay was defeated. It was a Pyrrhic victory however, and Dundee died having been hit in the eye with a musket ball. It was also, interestingly, the last battle at which the double-handed broadsword was used, to great effect.

Rob Roy later joined the Lennox Watch, effectively a paid band of Highlanders who protected the Lowlands. The payment was termed 'blackmail'. In 1693 he married Mary Campbell, who was from Comer, on the east side of Ben Lomond.

For a time his fortunes increased, gaining lands and becoming a cattle dealer. But in 1711 his chief drover, a MacDonald, absconded with letters of credit, and MacGregor was wrongly accused of embezzlement. A warrant for his arrest was issued, under the instigation of the Duke of Montrose, a main creditor, and on failing to answer the summons, MacGregor was outlawed.

For some time, he was forced to survive by the time-honoured pastimes of lifting sheep and cattle, particularly from Montrose's land. By now his wife and family had been evicted from Craigroyston by Montrose's factor, Graham of Killearn. MacGregor rented a property in Glen Dochart, Auchinchisallen, from the Earl of Breadalbane, who was a political opponent of Montrose. In 1715, he raised the clan MacGregor for the Jacobite cause. In the Callendar area he seized 22 government guns. He was at the dying moments of the Battle of Sheriffmuir, when inept leadership by Mar lost the day. An earlier decision not to be led into suicidal situations by incompetent Jacobite generals obliged him to make a tactical withdrawal with his men, but he had to suffer the burning of his home at Auchinchisallen by Swiss mercenaries. He had set up an ambush, but with barely a dozen clansmen against 60 Swiss troops he could not afford a battle.

By 1717, The Duke of Montrose was enraged and frustrated. He obtained a Commission to arrest MacGregor, and was fortunate in learning of his presence in a house at Balquhidder. At dawn he caught Rob Roy asleep in his plaid, and binding his hands took him on horseback towards Stirling.

At the Fords of Frew, over the Forth, the river that April was swollen and cold. His hands were released for his safety, but a leather cord attached him to the man in front, a James Stewart, one of Montrose's tenants. There are two versions as to what happened next. Either Rob Roy had a concealed armpit knife, and cut the thong himself, or Stewart, who had received some benefit from MacGregor in the past, released him on a whisper from Rob Roy.

Rob Roy jumped into the river, releasing his plaid, and swam away underwater. The plaid received much attention, including musket balls, and Rob Roy was able to gain the north bank in the gathering twilight. Once again he had escaped. It is fairly safe to say that from about now onwards, the Scots saw in MacGregor an heroic figure. There were many other stirring and true stories of his continuing struggle to find a peaceful and just life before he finally submitted to General Wade in 1725, gaining the King's pardon. He continued to work with his cattle business, offering protection to the Lowlands.

At the end of 1734, Rob Roy MacGregor was in his home at Inverlochlarig, at the head of the Glen of Balquhidder. All accounts are in agreement on his last words. 'It is all over. Put me to bed. Call the piper. Let him play Cha till me tuille.' While the piper played the lament I shall return no more, Rob Roy died.

He had, as was befitting, a great funeral in Balquhidder. All ranks, and most of the clans, were there. He was buried, Catholic or not, in the graveyard of the auld kirk at Balquhidder, under an ancient Celtic slab carved nearly 400 years earlier. It lies there still, its carvings almost faded, but showing a two-handed claymore and a warrior.