Baker will be co-captain in just his second season with the Eagles, while a new recruit has instantly joined the club's leadership group.
Ex-Brisbane premiership player Brandon Starcevich will be among the seven-strong leadership group, sitting below Baker and Duggan, who will skipper for a third consecutive season.
Starcevich is yet to play for the Eagles, while Baker won the club's best-and-fairest award last year - his first season in WA after seven at Richmond.
"Since joining the club, Liam Baker has had an immediate impact with his training standards, his ability to connect with teammates and all staff, and his communication and passion to see the club achieve on-field success," West Coast's head of football John Worsfold said in a statement on Thursday.
"It was no surprise he was seen as a worthy captain through the players' leadership vote.
"Co-captaincy will allow both players to mentor their teammates in the most effective way ... whilst still focusing on their individual preparation and performance."
Jake Waterman and another ex-Tiger premiership player Jack Graham remain in a leadership group with new additions Reuben Ginbey, Matt Flynn and recruit Starcevich.
"Brandon's leadership qualities have impacted our young squad immediately," Worsfold said.
"Coming from Brisbane's leadership group, he adds valuable nous and experience from within a two-time premiership squad.
"With that knowledge and his own quiet but strong values base, his teammates nominated him for their leadership group without question."
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