"I'm pleased to join one of the biggest Balkan clubs," the 28-year-old centre back, capped 40 times by Bulgaria, told local media. "I'm quite enthusiastic and I hope to have luck and no injuries."
Ivanov, Bulgaria's footballer of the year in 2013, suffered a series of injuries after joining Basel from Partizan Belgrade in 2013 and played only 18 times.
In December, he was released from the Swiss club by mutual consent and rejoined Lokomotiv three months later in a bid to resurrect his flagging career with the 2004 Bulgarian champions.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Panathinaikos, 20-times Greek champions, will join next season's Europa League in the third qualifying round.
(Reporting by Angel Krasimirov,; Editing by Neville Dalton)
