The 25-year-old, who was named Skrill North player of the year in 2013-2014, is joining John Still’s Hatters after plundering 28 goals for the Pilgrims last season.
Miller revealed earlier in the summer that he would sign a new contract at The Jakemans Stadium — unless an offer was forthcoming from a professional club.
Luton’s approach on the eve of pre-season means that Miller will be playing at Kenilworth Road in 2014-2015 as Town prepare for a return to the Football League.
United boss Dennis Greene told bufc.co.uk: “You cannot do anything but wish Ricky the very best of luck at Luton Town.
“He was fantastic for us last season and certainly deserves his crack at a higher level.”
During his two spells with the Pilgrims, Miller scored 34 times in 58 appearances — and moves on with the best wishes of everybody at Boston United.