Eriksen left Inter Milan in December by mutual consent after being barred by medical authorities from playing in Serie A.
He had an implantable cardioverter defibrillator fitted and has been passed as fit to return to football.
The uplifting signing was an early announcement on the final day of the January transfer window in the Premier League. Signing with Brentford until the end of the season, Eriksen is returning to England where he played with Tottenham until joining Inter Milan two years ago and winning the Serie A title.
The west London club will feel like home. Eriksen is being reunited with Thomas Frank, the Brentford manager who coached him when playing for Denmark's under-17s team. He will also be the ninth Dane in the club's squad.
“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.”
Frank will be hoping Eriksen provides a further lift for a team impressing in its first-ever campaign in the Premier League, sitting eight points above the relegation zone with 15 games remaining.
“At his best, Christian has the ability to dictate games of football," Frank said. "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."
Eriksen was recently training to regain fitness at Ajax, the Dutch club where he began his career.
Brentford said it would “respect Christian’s medical confidentiality” by not divulging further information beyond saying he only recently received coronavirus vaccines that allow him to comply with entry rules to Britain.