This purchase agreement, which follows a letter of intent signed late last month, includes commitments for 25 MAX 7 and 40 MAX 8 aircraft with substitution rights to the 737 MAX 9.
Deliveries are scheduled from 2017 through 2027, WestJet said Thursday.
Financial details were not available.
WestJet said it will substitute 15 of its existing Boeing Next-Generation 737 aircraft orders currently scheduled to deliver between December 2014 and 2018, with Boeing 737 MAX aircraft, for a net increase of 50 committed deliveries to its fleet plan.
"We are pleased to announce the finalization of the MAX purchase agreement and look forward to being among the first North American airlines to fly the 737 MAX in 2017," said WestJet president and CEO Gregg Saretsky.
"The increased fuel efficiency and enhanced in-cabin amenities provided by the Boeing 737 MAX will contribute to both lower operating costs and a remarkable inflight guest experience. . . . "