As a child Mellor was schooled at Lepton County Primary School, King James's School at Almondbury and Greenhead College.
According to Canon Hulbert of Almondbury in Yorkshire, the 28-year-old was an intelligent young man who had ambitions beyond the linen trade: "Slaithwaite was scarcely a sufficient sphere for his genius and he emigrated to the United States, where he took up the then infant Art of Photography; which he much improved by his experiments and discoveries."