The 24-year-old Wales international swaps North London for South London in a club-record deal, reported to be worth £35M, which is a club record for the Eagles.
Johnson leaves Spurs after two years, having joined the club from Nottingham Forest in September 2023 for a fee in excess of £45m.
The deal was announced on Friday afternoon as manager Oliver Glasner welcomed him to the club as per the club website.
"I’m really delighted that Brennan has joined the club. He arrives very early in the window, so credit to the club for making this happen so quickly.
"Brennan will give us options in our attacking play with his pace and goal scoring ability, and with all the upcoming games he will be a valuable addition to the squad."
Johnson delighted with the move
Johnson, who bagged the winning goal In Tottenham's Europa League victory over Manchester United in Bilbao, also revealed how happy he is to pull on the shirt.
"I'm really excited and I'm really happy. Crystal Palace are such a great club, one that I've always admired.
"It's a great time for me to be here and join the journey that this club is on – I'm super excited."
Tottenham wished Johnson well for the future as they waved goodbye to the player who ended their trophy drought.
“We thank Brennan for his contribution and wish him well for the future.”