Heidfeld took over after Robert Kubica sustained a career-threatening injury in a rally-car accident in February.
But the German driver was replaced for the Belgian Grand Prix last weekend by Senna, whose uncle was the late Brazilian F1 great Ayrton Senna.
Renault team principal Eric Boullier said Friday a "swift and reasonable solution" was reached with Heidfeld. Boullier added that the "separation process was already a painful one, and neither of us wanted to go through another legal hearing."
Senna made his F1 debut with Hispania Racing last season and started the season as a reserve driver for Renault.