His early life is, at the moment, completely obscure and he only appears on record in 1588 when he rose to the rank of sergeant major in the regiment of Colonel Bartholomew Balfour.

However, after some confusion, they heard that the guard in the town had been doubled and the captains decided to call off the attack, Brog insisting he would not "lead his men to certain butchery.

"[3] In 1595, Brog was specially appointed as sergeant-major to an auxiliary force under Justinus van Nassau to relieve Cambrai in a joint effort with Henry IV of France.

[6] In February 1602 a rumour circulated that the exiled rebel Earl of Bothwell had left Spain for the Low Countries and was trying to bribe Colonel Edmond or Brog, (who were said to be rivals in emulation), with their Scottish soldiers to join the Spanish service.

Perhaps the Earl also assumed he would take command of his father's regiment in 1612 after the Lord's death, but was instead passed up for the far more experienced Sir Robert Henderson.

Brog came to the Hague from Scotland in January 1622, and Dudley Carleton wrote to the Duke of Buckingham that he was "most unwilling" to be pensioned off.

[11] On 30 September 1622 Frederick V of the Palatinate wrote to Elizabeth Stuart, Queen of Bohemia that "Colonel Brog will leave his regiment most reluctantly; but still it needs to be reformed.

[citation needed] On 4 November 1631, Colonels William Brog, Sir David Balfour, and George Coutts intervened on behalf of the widow of Reverend Andrew Hunter for a pension of 100 guilders.