Sean has shoulder-length ginger hair, green eyes and is slightly unshaven. He appears to be missing a few of his upper teeth. MacGuire usually wears a jacket of a light bluish-grey color over a dirty white union suit and a red and brown patterned vest, accompanied by blue jeans and a green bowler hat. Unlike most members, this is the only clothing he wears, with only slight variations.

When Sean is rescued from Ike Skelding's Boys, he is shown wearing black jeans held up with suspenders, along with a grey shirt buttoned at the top with a black square shape on the front going from the shoulders to the chest, as well as black cuffs.