Four British Typhoon jets arrived in Lithuania to start their mission while four French Rafale jets touched down in Malbork, northeast Poland, their defense ministries said.
British defense minister Philip Hammond said the move would "provide reassurance to our NATO allies in eastern Europe and the Baltic states."
"In the wake of recent events in Ukraine, it is right that NATO takes steps to reaffirm very publicly its commitment to the collective security of its members," Hammond said.
Around 70 French military personnel have been deployed to Malbork in support of the new planes, French military spokesman Colonel Gilles Jaron said.
Britain and France have each also deployed AWACS early-warning aircraft to patrol Polish and Romanian airspace in recent weeks.
The Baltic states of Latvia, Lithuania and Estonia, which gained independence from the former Soviet Union in 1991, joined NATO in 2004 but lack sufficient aircraft to police their own skies, so larger NATO members take turns patrolling their airspace.
NATO announced in April that it would step up its defenses in eastern Europe due to the growing crisis in Ukraine.
It has increased fighter jet patrols and also deployed ships in the Baltic Sea and eastern Mediterranean.
The United States announced last week it was deploying 600 airborne troops for exercises in Poland, Latvia, Lithuania and Estonia in a show of solidarity with NATO members bordering Russia.
RA/NJF