Midfielder Procter has played for Accrington since 2002
New Preston boss Graham Westley has signed Andy Procter, Chris Holroyd and Jamie McAllister.
Procter, 28, has initially joined on loan from Accrington, and will sign a two-and-a-half-year deal on Monday for an undisclosed fee.
Striker Holroyd, 25, has signed an 18-month contract after moving from Rotherham for an undisclosed fee.
Bristol City defender McAllister, 33, has joined on a one-month loan after recovering from an ankle injury.
Stanley captain Procter played over 400 games for the club, picking up the fans', players' and manager's player-of-the-year award last season at the Crown Ground.
Holroyd spent nine years coming through the successful youth set-up at Crewe, and also featured in Gus Poyet's Brighton & Hove Albion League One winning squad before joining the Millers.
He previously played under North End boss Westley at Stevenage.
Former Queen of South, Aberdeen, Livingston and Hearts man McAllister has played for Bristol City for five and a half seasons, featuring 203 times.