The Toffees rushed to tie down the Ukraine international until 2029, as his current deal was set to expire in June 2027.
Mykolenko has played a key role at Everton since joining the club in January 2022, making 158 appearances in all competitions, including 36 during the last campaign.
While the 27-year-old divides opinion among the fanbase, he's undoubtedly highly rated by David Moyes, and this new deal represents his faith in the left back.
“I feel excited to sign this new contract – very excited and proud," Mykolenko told Everton TV.
“I remember the first message I received from Seamus (Coleman) when I signed in 2022. I remember reading it and thanking him for welcoming me. He gave me that confidence immediately that I'm in a proper family here.
“In the first few years of my time here we were struggling, but our team, as a family – every person in the building gave everything to get through it. What we have now is stronger and we are getting better every season.
“For me, it's most important to feel confident and feel comfortable in the environment and I have that here, so I’m really happy.”
Mykolenko credits Everton legend Seamus Coleman for welcoming him to the club over four years ago and instantly instilling confidence in him.