Garrick was a sergeant of The Legion and was Cruniac's second in command.
Following his commander's death, he took command of the The Legion. Garrick and the Legion managed to evade Soulblighter via the World Knot and arrived in Madrigal to warn Alric.
Following The Legion's withdrawal from Madrigal, Garrick led the Legion at White Falls to deny Soulblighter access to the northern cities. It is conceivable that Garrick was of lower ranking and statue compared to Baeldun, commander of the 7th Legion.