Inter Milan were forced to part ways with him last summer, with Serie A rules stating he wasn't allowed to play with an implantable cardioverter defibrillator (ICD) device fitted.
However, after passing all the medical examinations at Brentford, the 29-year-old has signed a deal running until the end of the season.
Brentford boss Thomas Frank was keen to see his compatriot join the club on Deadline Day, and is hoping to see him return to his former heights.
"We have taken an unbelievable opportunity to bring a world-class player to Brentford," Frank said. "He hasn't trained with a team for seven months but has done a lot of work on his own.
"He is fit but we will need to get him match fit and I am looking forward to seeing him work with the players and staff to get back towards his highest level.
"At his best, Christian has the ability to dictate games of football. He can find the right passes and is a goal threat."
After training with former club Ajax for the last couple weeks, Eriksen completed the deal in Amsterdam and will join up with the rest of the squad in the coming days.
"I can't wait to get started and hopefully I'll seen you all very soon," Eriksen said in a short video on Brentford's website.
While the club naturally kept Eriksen's medical information private, Brentford's director of football Phil Giles has said, "Brentford fans can rest assured that we have undertaken significant due diligence to ensure that Christian is in the best possible shape".