The 23-year-old will bolster the attacking options for head coach Graham Potter, whose squad is currently beset by injuries.
Here we take a look at what the player will bring to the London club.
Point to prove
Felix joined Atletico in a much-heralded £112million move from Benfica in 2019, but has struggled to live up to such a massive price tag. After helping Atletico win LaLiga in 2020-21 – their first title in seven years – Felix has now dropped down the pecking order for boss Diego Simeone.
Felix, who scored in Portugal’s opening game at last year’s World Cup, will be out to prove his doubters wrong with a run of consistent form in front of goal for Chelsea, who are in need of a spark to kick-start their campaign.
Felix is not a traditional centre-forward and brings more to the party than just leading the front line.
In Qatar, Felix was often deployed on the left wing by then Portugal boss Fernando Santos, which allowed him to provide an outlet through the transition and also to quickly cut inside to further stretch the opposing defence.
Expect Potter to make similar use of Felix’s flexibility from the wing to the centre to help reboot an attack which has lost the likes of Raheem Sterling and Christian Pulisic to injuries.
A short-term fix
Chelsea are expected to further bolster their attacking options in the summer with a £50m-plus move for RB Leipzig’s Christopher Nkunku, the France forward who is currently recovering from a knee problem.
That, though, will be little help to Potter in the here and now as his own position comes under scrutiny. Felix at least provides someone they will hope can hit the ground running and lift the mood as the Blues look to work their way back up the Premier League table.