The 26-year-old Russia international will now undergo a medical ahead of a potential move back to his homeland.
Bilyaletdinov has failed to make a big impression since his near-£9million to Goodison Park from Lokomotiv Moscow in 2009.
A statement on the club's website read: "Spartak have reached an agreement in principle with the English [club] Everton and 26-year-old midfielder Diniyar Bilyaletdinov for a transfer to our club.
"The contract will be signed after the medical examination."
Bilyaletdinov took time to settle on Merseyside but showed potential during his first season at the Premier League club, scoring seven goals.
He failed to build on that promise and has been unable to command a regular place in David Moyes' side.
He has started just seven league matches this season and was an unused substitute in Saturday's 1-1 draw with struggling Blackburn.
Bilyaletdinov's departure would be Moyes' third major piece of business of the January transfer window after the signings of forward Landon Donovan, on loan from the Los Angeles Galaxy, and midfielder Darron Gibson from Manchester United.
