Gilbert LaFayette Parker was born on December 19, 1832, in Harrisburg, Pennsylvania, to Gilbert S. Parker and Pennina Duncan. His father was an insurance company president. By 1860, Parker was working as a clerk in Philadelphia, Pennsylvania.
On July 6, 1861, he received a commission as a 1st lieutenant in Company D of the 28th Pennsylvania Infantry. The regiment took part in the Second Battle of Bull Run and the Battle of Antietam. On April 7, 1863, he was promoted to captain and assistant quartermaster. He received a brevet promotion to lieutenant colonel on March 13, 1865, and he mustered out on June 30, 1866.
He returned to Philadelphia after the war, and he married Mary Cox. They had at least three children: Gilbert, born around 1870; Annie, born around 1871; and Earnest, born around 1875. He graduated from Jefferson Medical College in 1874 and earned a living as a physician. According to one local writer, he “not only gained the confidence and esteem of a large number of patients, whose sufferings he has alleviated by his ability and skill, but he has also attained a high position among the members of the medical profession.” He died of “cirrhosis of the liver” in Philadelphia on May 19, 1915.