From 1849 to 1851 Marshall was the principal of Fitchburg High School in Massachusetts.

[2] Marshall studied law with the firm of Torrey & Wood in Fitchburg, Massachusetts, and in Concord, New Hampshire, with Franklin Pierce and Josiah Minot.

[2] On the Fourth of July, 1874, Marshall, his wife and son were setting up a picnic lunch at Penacook Lake in West Concord when his wife heard the sound of bullets over their heads.

Marshall saw no one firing, shouted to the shooters to be careful, then stood up and was shot in the abdomen.

[3][4] Marshall was shot with a minnie ball[3] fired by the City Guards,[3] a newly formed[3] militia company[2] that was engaged in target practice in a pasture bordering the lake.