Passengers with platinum status in the Belgian airline’s Privilege frequent flyer initiative will be allowed to use Lufthansa’s senator and business class lounges across the world.
Lufthansa passengers who have signed up to the Miles & More scheme will benefit from access to Brussels Airlines’ range of lounges.
Announcing the agreement, a Lufthansa statement said that the next steps of the partnership "are already underway".
"Passengers will very shortly be able to combine the fares of the two carriers in cross-border traffic," it said.
"Conclusion of a code-share agreement encompassing large parts of the two airlines’ networks is also envisaged."
It was also revealed that Swiss International would pool its frequent flyer programme in line with Lufthansa and Brussels Airlines.
Lufthansa regional subsidiary airline CityLine will begin a new flight to Rzeszow from Frankfurt on April 27th.