The Scotland international has signed a four-year deal after he terminated his contract with the soon-to-be-liquidated Scottish side, having rejected the chance to move over to the newco club.
Naismith, 25, will now join up with his new team-mates for the start of pre-season training this week.
"It is a great honour to be joining a club of Everton's wonderful history and to have the chance to play with such a talented group of players in the world's best league in front of such a passionate group of fans," Naismith told evertonfc.com.
"I look forward greatly to working with the manager David Moyes and all the staff at Everton and working hard to deliver on the pitch to repay their, and the chairman Mr (Bill) Kenwright's, faith and belief in me."
Moyes was keen to add greater strength to the forward line and believes Naismith will fit in well at Goodison Park.
"We are delighted that Steven has agreed to join us," said the Scot. "He will be an excellent addition to the players we already have and we look forward to him being fit and ready to play at the start of the season.
"He is an established international who can play in a number of positions.
"He has a flexibility we always like in our players and which will hopefully prove to be very useful for us."