At some point he moved to Ann Arbor and attended Law School at the University of Michigan before graduating in its first class in 1860.

[3] He then participated at the Little Round Top where Welch and the 16th Michigan made a defense during the engagement with only 150 men against John Bell Hood's divisions of Texans and Alabamians.

During the battle, he and the 16th Michigan would approach an entrenched Confederate as he reportedly leaped his sword in hand and shouting at his men "On boys and over!"

[4][6] His bravery at Peebles's Farm restored his reputation as Joshua Lawrence Chamberlain commented: Among these men were some doubly deserving—comrades whom we thought lost, bravely returning.

Welch, of the 16th Michigan, first on the ramparts at Peebles’ Farm, shouting, ‘On boys, and over!’ and receiving from on high the same order for his own daring spirit.