His paternal grandfather, Alexander Grant, was a veteran of the Battle of Culloden of 1746 who later became a director of the East India Company and was the last man to escape from the Black Hole of Calcutta.

Despite his young age, with the influence of his cousin Charles Grant, 1st Baron Glenelg, he was named the surgeon for the General Stuart.

Just before leaving on his maiden voyage, Grant married Margaret Urquhart, the daughter of an East India Company official.

[3] He was soon a member of the Texian Army, serving from December 1835 through March 1836, during the Texas Revolution and fighting in the Siege of Bexar.

In early December, Grant was advocating for an expedition to invade Matamoros, suggesting Houston was not the person to be in charge of the Texian Army.

In Refugio he approached the soldiers, telling them how a small army could not conquer a city of 12,000 and thereby convinced over half of the men to quit.

Splitting into smaller groups, the Texians searched for mounts and supplies, proceeding all the way to Santa Rosa Ranch.

Grant and a group of fifteen Texians while foraging, were attacked by members of General José de Urrea's cavalry.