The striker completed the move on Thursday and is eligible to go straight into the Leeds squad for their home game against Bournemouth on Saturday.
The move completes a surprising U-turn from the Scotsman, who earlier in the week said he had no intention of switching to Elland Road.
However, after it was made clear that first team chances at Palace would be extremely limited, Freedman has decided to test himself elsewhere.
"I had a conversation with Neil [Warnock] on Wednesday and he feels I'm not going to play much of a part in the rest of the season," Freedman told the Croydon Advertiser.
"He is building for next season and I understand that - but not playing games isn't good to me, so I've decided to go to Leeds.
"Palace are in my blood and if I go to Leeds, play some games and help them get promoted then hopefully I can come back to Palace and show him that he shouldn't have let me go."
Dougie Freedman is regarded as a club legend by the Palace faithful, scoring 108 goals in 368 appearances during his two spells at Selhurst. However, this season he has been restricted to just four starts and 15 substitute appearances.
No matter how things go for him and Elland Road, Palace fans will still get at least one more chance to see him turn out in red and blue colours as he has been promised a testimonial match in the summer.