The defender had been linked with a return to Middlesbrough, but will now spend the season on loan at Fulham.
Kalas spent 18 months at Middlesbrough
The 23-year-old spent 18 months at the Riverside, where he was part of an impressive defence that conceded a league-low of 31 goals last season, helping Aitor Karanka's side secure automatic promotion on the final day.
The defender will spend the coming season on loan at Fulham
The Daily Mail recently claimed that the Teessiders were keen on bringing the Czech international back to the club, with another season-long loan deal mooted.
But the move to west London has put any speculation of a return to the north east to bed.
Kalas impressed for Boro last season
Fulham are the fifth team to take Kalas on loan since he made the switch to Chelsea in 2010 as a 17-year-old, with previous spells at hometown club Sigma Olomouc, Vitesse Arnhem and FC Koln.
Kalas will be hoping to get some more experience under his belt at Craven Cottage
Kalas has subsequently made just four senior appearances at Stamford Bridge, and the competition provided by Gary Cahill, John Terry, Kurt Zouma, and Matt Miazga, means was unlikely to add to that total this season.