The 29-year-old Denmark international has not played since suffering a cardiac arrest at last summer’s European championship.
Eriksen was fitted with an implantable cardioverter-defibrillator device which prevented him from playing for Inter Milan and had his contract with the Italian champions mutually terminated as a result.
The former Tottenham Hotspurs playmaker had been training with Odense and recently the youth side of Ajax Amsterdam but has now returned to the Premier League on a short-term contract as he aims to get a call up for Denmark’s FIFA World Cup campaign in Qatar later this year.
In a video posted by Brentford's official Twitter account, Eriksen said: "I'm happy to announce that I've signed for Brentford football club. I can't wait to get started and hopefully I'll see you all very soon."
Brentford boss Thomas Frank added on a player he once coached in the Denmark youth sides: "I am looking forward to working with Christian again. It has been a while since I last coached him, and a lot has happened since then.
"Christian was 16 at the time and has become one of the best midfield players to appear in the Premier League. He has also won trophies all over Europe and become the star of the Danish national team.
"We have taken an unbelievable opportunity to bring a world-class player to Brentford. 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. He also has very, very good set-piece delivery, both from corners and direct free kicks.
"He is a player you can find with the ball, and he will come up with a solution to the problem in front of him. Christian will also bring experience of top-level football to the club. I expect him to have an impact in the dressing room and at the training ground."
