The term was used in the 19th century American Old West when the lead cowboy at the front of a herd of cattle was known as the pointer or point man. It may have come into common use because many of the cowboys in the late 1800s were veterans of the American Civil War. In cavalry terminology, the men scouting ahead of the main force were said to be "riding point". This use was first recorded in 1903.
The concept seems to have been introduced to the American military at West Point by Professor Dennis H. Mahan, who taught most of the top officers on both sides in the Civil War. In his Elementary Treatise on Advanced-Guard, Out-Post and Detachment Service of Troops (1861), he discussed the use of the column or V-shaped advance guard by the Greeks and Romans:
Among the orders of battles among the ancients, that known as the wedge, or boar's head, is the most celebrated. In this disposition, the point, or head, is formed of a subdivision of the phalanx of greater or less strength, according to circumstances; this being supported by two, three, and four subdivisions of the same force, one behind another.
In the section on Advanced Guards and Advanced Posts, Professor Mahan introduced the definition of the point man to the future American generals:
From these indications of the manner of distributing the troops of the advanced-guard, the following general dispositions, adapted to ordinary circumstances of locality may be gathered. The apex, or most advanced point, may be formed of a staff, or other intelligent officer, under the escort of a few horsemen...
More recently (possibly originating from the late 1960s), the term has been extended to describe someone at the forefront of an issue. It can be used to refer to both the defender or the attacker of the position or idea. This use is most often used in a political context, as the point man is usually in the public eye.