The 25-year-old backman has been in outstanding form this season after missing rounds two and three with a hamstring injury.
As well as keeping Coleman medallists Jack Riewoldt and Jonathon Brown to just two goals each in matches against Richmond and the Brisbane Lions respectively, Mackenzie was the unlikely match-winner at the other end of the ground in the Eagles’ last-gasp win over St Kilda in round 11.
Having kicked just one goal in his previous 87 games, Mackenzie bobbed up with two against the Saints, including the sealer after running the length of the ground from full back deep in the final quarter of West Coast’s four-point win.
"It’s great to have the contract out of the way by this stage of the season,” Mackenzie said.
"It will allow me to concentrate purely on what needs to be done in the second half of the year.
"As a team, we have great improvement in us and we are determined to have an impact over the next couple of months.
"We need to play consistently good football to achieve our targets and that is definitely possible.
"We start with a big challenge against Hawthorn, but matches like these are the reason we all play."
Mackenzie was recruited from Claremont with pick 29 in the 2006 National Draft, and his contract extension will see him beyond 10 years at the club.
West Coast list and contracts manager Craig Vozzo said the club was delighted to have re-signed Mackenzie.
"Eric is a terrific person and a very important part of our football club," Vozzo said.
"He is an outstanding player who is fast becoming one of the premier defenders in the game.
"He has learnt a lot about playing on the power forwards by studying and talking to Darren Glass and he is very accomplished.
"It is good to have a player of Eric signed for the next four years.
"He will certainly be a key element of our defensive structure in both the short and medium term."
