The 25-year-old striker has cost West Ham around £9m. A late bloomer, he started his career in non-league with sides like Seaham Red Star, Consett and Whitby Town and also had a spell at the Glenn Hoddle Academy before moving to Port Vale who still retain a 20% sell on fee.
Hugill has scored 10 goals in 29 games for Preston so far this term. The Hammers are expected to announce the signing on the official website soon.