The left-back is out of contract at Stevenage this summer and has rejected a new deal at Broadhall Way, with the switch to be completed on July 1.
Laird, who has agreed a two-year deal at Deepdale, spent the best part of four years under Westley at Boro before the latter's managerial switch to North End in January.
And Laird has now opted to rejoin his former boss as Westley reshapes his squad for an assault on League One promotion next term.
The 24-year-old said: "When Graham showed a bit of interest and wanted to bring me here I was chuffed. I had already made my mind up to come to Preston. It is steeped in history and even looking around the ground it is an amazing facility."
Laird becomes Preston's eighth summer signing after John Welsh, Nicky Wroe, Shane Cansdell-Sherriff, David Buchanan, Paul Huntington, David Amoo and Richard Wright.