To be an IFBB pro you need to be offered an invitation from the IFBB. They can hand out an invitation to anyone they want, but winning certain contests will get you an automatic invitation.
Limiting ourselves to the men, automatic invitations include winning your class at the NPC Nationals (7 invitations), winning the overall at the NPC USA, winning the overall at the IFBB North American, winning the overall at the NPC Team Universe.
Outside the US, winning your IFBB national championships should be enough, but they are very inconsistant. Winning the IFBB Worlds should get you a pro card, but if so, most choose not to accept it. In the last 10 years, only
Ahmad Haidar,
Jaroslav Horvath, and
Dennis Wolf won the worlds and went on to be a pro.
in another thread, we were talking about amatuer vs pro.
Hamdullah Aykutlu and
El Shahat Mabrouk competed as pros in the IFBB and then later went back to competing as amateurs in the IFBB Worlds.
regarding current pros, how and when did
Hidetada Yamagishi get his pro card? His best showing at the Worlds was 6th in 2000. He won the overall Japan Nationals in 2001 and his class again in 2002.
Silvio Samuel Saviour won a whole bunch of NAC and WABBA contests, but I have no record of him ever entering an amateur IFBB event, certainly not the Worlds.
Tamer El Shahat won the IFBB Egyptian Nationals, but was DQed from the Worlds for failing the drug test (had been third). He also won Musclemania.
Mohamad Moussawi was living in southern California, won the NPC California, placed 6th at the NPC Nationals, then moved to New Zealand, won their Nationals (but supposedly failed the drug test), and now he's a pro.