Samuel had been a free agent after leaving Bolton and failing to impress on trails with Leeds United and West Ham.
The 30-year-old's last game was on loan at Cardiff in the second leg of their Championship play-off defeat to Reading at the end of last season.
Speaking to Sky Sports News, Samuel explained how the surprise move, on a five-month contract, came about: "It was through a friend who had the contact, I had a look at it and it seemed to add up for myself.
"Obviously it's a new challenge, something out of the ordinary but I'm willing to take that chance.
"They are one of the biggest clubs in Iran, they have 100,000 people watching their derby games and the fans here are unbelievable really."
He will be reunited with former Bolton team-mate Andranik Teymourian who joined Esteghlal in July.
And Samuel says the midfielder has told him a lot about football in Iran.
"When I was at Bolton Andranik talked about it quite a bit and he's playing here now but he's injured at the minute."
Samuel claims there was interest from clubs in England, but the lure of the Asian Champions League proved to be a major draw.
"I did have options to stay in England, and I had offers from quite a few teams abroad but for me this is a new challenge and a chance to enter the Asian market.
"This team plays in the Champions League here."
