Kalas has spent the last 18 months on loan at Middlesbrough and the north east club had hoped to land him permanently this summer.
However, the 23-year-old, who has made four appearances for Chelsea since arriving in 2010, has opted for a loan a little closer to home.
And the centre-back, who can also operate on the right side of defence, reckons his new club are capable of winning promotion back to the Premier League.
He told the club’s official website: “Hopefully promotion or at least play-offs. When I was at Middlesbrough nobody expected us to get to the play-offs and we got there.
“After the last two seasons, nobody expects Fulham to be that high but why not? After two bad seasons should come a better one.
“Fulham were really active, trying to reach me and call me. I could really see that the club wants me.
“I’m quite happy then to sign because when you see the interest that’s one of the most important things.”