Kennedy and Hurn have combined for 557 games and five All-Australian selections in their time with the club, both being prominent features in the Eagles' 2018 premiership-winning side.
With West Coast understood to be facing a tight salary balance for next year, deals for the star pair were delayed until the off-season.
It is understood that defender Jeremy McGovern has accepted a pay cut for next season, sacrificing close to $200,000, which will likely be relayed to the latter stages of his current contract.
The decision has aided the club's finances and planning for the future, with Hurn, Kennedy and O'Neill having now re-signed.
Hurn, who sits as the club's record games holder and is the first Eagle to surpass 300 games in the blue and gold, will enter a 16th season at the club.
'Bunga' led the Eagles to their grand final victory over the Magpies three years ago before stepping down as skipper at the end of the 2019 season.
The Eagles' all-time leading goalkicker with 675 majors, Kennedy has been a fruitful recruit for the Western Australian club.
O'Neill, who was also out of contract for next season, has signed for a further two years in hope of adding to his 13-game tally for the Eagles.
The 21-year-old made his debut in 2020, playing five matches in his rookie season.