McCullum took charge of the Test side in 2022 and transformed England's fortunes with his attacking 'Bazball' approach, winning 11 of his first 13 Tests.
However, England have won only three of their last 12 Tests, including a recent 2-1 home series defeat to New Zealand following a 4-1 Ashes loss in Australia.
ECB chief executive Richard Gould said "the time is right to make a change" as England begin preparations for next summer's Ashes, while managing director Rob Key will remain in his role.
McCullum said he was "gutted" to leave the Test job but respected the decision.
"I've absolutely loved coaching the Test side and I'm incredibly proud of what we've achieved together. It's been a privilege and an honour."
"Of course I'm gutted not to be continuing, but I respect the decision. My focus now is on giving everything I've got to the white-ball teams."
The 44-year-old took over England's white-ball teams in 2025 and recently guided them to the top of the ICC T20I rankings after a 4-0 series sweep over India. He remains under contract until the end of the 2027 ODI World Cup.
England must now appoint a new Test head coach and captain following Ben Stokes' retirement from international cricket.
