Ellis, 23, has agreed a four year deal with the Rhinos after the clubs agreed an ?undisclosed substantial fee?.
Ellis, who was part of Great Britain?s Gillette Tri Nations squad, has been awarded the Rhinos? number 20 squad number which had been left vacant when the initial squad for 2005 was announced.
Ellis was at Headingley on Boxing Day for the Tetley?s Festive Challenge between his former club and his new one, although the deal to bring him to Headingley was only concluded in the past 48 hours following that game.
The deal is the same one that was offered over a month ago and has been agreed with both Wakefield and Ellis.
Commenting on the signing Leeds? Chief Executive Gary Hetherington said: ?I am delighted that a player of Gareth?s calibre has agreed to join us. We are building something special here at Headingley and to sign a Test player who has already played over 100 games in Super League but is still only 23 is great for us. I would like to thank Wakefield for the professional manner in which the transfer has taken place.?
Head Coach Tony Smith added: ?I am really excited about the signing. As much as Gareth has already achieved in his career, he also has so much potential to fill and I am looking forward to working with him.
"He is a player we have admired for a while and it is great that he sees his future here with the Rhinos. We had always hoped that he would want to join us and I have been impressed by his determination to succeed and achieve at the highest level. He will now join up with the squad along with our other seven players who were involved in the Tri Nations.?
Ellis commented: ?It is a great move for me. Leeds is such a big club and I can?t wait to get started. I have a lot of respect for Wakefield and I thank the club and supporters for their support over the years - I will always be grateful to them.
"This move will give me the opportunity to play at the highest level and hopefully win further honours. I was at Headingley on Boxing Day and saw the ovation the players received from the fans when they were parading the trophy and it would be special to be part of that.?
The Rhinos travel to York City Knights on Monday 3rd January to play their second pre-season fixture. The game will be played at York City?s Bootham Crescent and Ellis will be officially unveiled to the Rhinos supporters before the game.