[1] He graduated from Princeton in 1849, read law with William Ross of Frederick, and finished his legal degree at Harvard.

Johnson preferred not to join the newly forming Virginia regiments, arguing that Marylanders should fight under their own flag.

[2] On May 17, 1862, the initial 12-month term of duty of C Company, 1st Maryland Regiment, expired, and the men began to clamor for their immediate discharge.

Johnson reluctantly agreed with the men, but he could not disband the entire regiment in mid-campaign, and discontent began to spread.

Tell them this, and see if you are not spurned from their presence like some loathsome leper, and despised, detested, nay abhorred, by those whose confidence you have so shamefully betrayed; you will wander over the face of the earth with the brand of 'coward', 'traitor', indelibly imprinted on your foreheads, and in the end sink into a dishonored grave, unwept for, uncared for, leaving behind as a heritage to your posterity the scorn and contempt of every honest man and virtuous woman in the land.Johnson's speech seems to have worked where threats had failed, and the Marylanders rallied to the regimental colors, seizing their weapons and crying "lead us to the enemy and we will prove to you that we are not cowards"[4] At the Battle of Front Royal, May 23, 1862, the 1st Maryland (CSA) was forced into battle with their fellow Marylanders, the 1st Regiment Maryland Volunteer Infantry (USA) commanded by Colonel Kenly.

[5] After the Confederate victory at the First Battle of Winchester, Johnson, who was described by J. J. Goldsborough as "one of the handsomest men in the First Maryland", was the recipient of some not entirely welcome female attention.

According to Goldsborough: having dismounted from his horse in an unguarded moment, [he] was espied and singled out by an old lady of Amazonian proportions, just from the wash tub, who, wiping her hands and mouth on her apron as she approached, seized him around the neck with the hug of a bruin, and bestowed upon him half a dozen kisses that were heard by nearly every man in the command, and when at length she relaxed her hold the Colonel looked as if he had just come out a vapor bath.

[7]Johnson saw service in the Seven Days Battles in 1862, part of the Peninsula Campaign, a series of six major battles over the seven days from June 25 to July 1, 1862, near Richmond, Virginia, in which Confederate General Robert E. Lee drove the invading Union Army of the Potomac, commanded by Maj. Gen. George B. McClellan, away from Richmond and into a retreat down the Virginia Peninsula.

As commander of the post at Salisbury, N.C., he used his influence to lessen the suffering among the prisoners of war and finally obtained their parole.

William Carter Knight and Patrick Henry Starke declared their run for the Virginia Senate on the Sunday before election day.

After the death of his wife, he moved to Amelia, Virginia, where he died, but his remains were interred back in Baltimore in Loudon Park Cemetery.