Last year, the Finn's teammate Felipe Massa withdrew from the body for personal reasons, while his championship rival Lewis Hamilton, as well as Force India's Adrian Sutil, refused to join the GPDA.
Prior to the Melbourne season opener last month, however, it emerged that Hamilton became a member on the persuasion of his McLaren teammate Pedro de la Rosa, who is GPDA president.
It was subsequently reported not only that Brazilian Massa, 27, rejoined the body in 2009, but also that reigning world champion Hamilton and his close friend Sutil have finally become members.
Rookie Sebastien Buemi has also signed up, as has BMW-Sauber third driver Christian Klien.
The GPDA is designed to give an influential voice with F1's ruling authorities about the concerns of drivers, ranging from safety matters to issues such as the cost of their mandatory licenses.