Mortimer began his artistic studies at Saint Martin's Lane Academy under Thomas Hudson. Later he studied with Robert Pine and Sir Joshua Reynolds. These teachers, especially Hudson and Reynolds helped shape the artistic temperament of the young Mortimer. He quickly excelled in his studies, receiving great praise from his teachers and peers. By the time he was twenty-three years old, Mortimer had won numerous prizes for his drawings and paintings and was considered one of the rising stars of British art. In 1774, he was made president of the Society of Artists of Great Britain to whose exhibitions he was a regular contributor.
Although Mortimer was a versatile artist whose range included portraiture, etching, book illustration, and Arcadian landscapes, he was primarily a painter of historical subjects. Mortimer's fluid and graceful brushwork in this pair of paintings reflects perhaps the influences of Sir Joshua Reynolds on the younger artist. Sadly, Mortimer's promising career was cut short by his untimely death at the age of thirty-nine.
The pair of paintings, The Black Prince Receiving King Johnand The Battle of Poitiers, had traditionally been ascribed to Benjamin West, who had painted these subjects for King George III. At the Battle of Poitiers, which took place September 19, 1356, the English under the Prince of Wales, who was known as the Black Prince, routed a much larger French army and even succeeded in capturing the French King John? This particular painting of the pair shows the pitched battle between the British and the French.