Newcastle have completed the signing of Mark Viduka on a two-year contract with the option of a third year.
Viduka scored 19 goals for Boro in the 2006-2007 campaign
The 31-year-old, who arrives on a free transfer, rejected a new contract offered by Middlesbrough.
"I'm over the moon - the main thing that attracted me to the club was that it is moving in the right direction," Viduka told the club website.
"Manager Sam Allardyce has come in and if we can get success then it will be something special."
He added: "Talking to Sam was a big turning point for me.
"I really wanted to hear what Sam's plans were for the new season and what players he was looking to bring in.
"And his answers matched with what I was thinking myself.
"I want to win things and Newcastle United is a club that has all the ingredients to do that, especially with Sam coming in."
Allardyce added: "We are getting a player with vast experience in Premiership football and a natural goalscorer.
"He has the size and stature to lead our front line and is direct competition for Shola Ameobi, who is fit again now.
"It is common knowledge that every manager in the game wants two players for every position, and that is what we will have at Newcastle United next season as far as our strikers are concerned.
He has the size and stature to lead our front line
"It is a great start for us as we already have Oba Martins and Michael Owen who can play off a big man. It is all looking very exciting."
Boro boss Gareth Southgate said he was disappointed to see Viduka leave the Teesside club.
"It is a regret for me, but we did everything we could as a club to try and keep him," he said.
"The fact that he was in the latter months of his contract was difficult. It meant he was able to speak to other people, but there was nothing more from that period on that we could have done."
Premiership sides Portsmouth, West Ham and Birmingham were also linked to the Australian.
Viduka was signed by Middlesbrough from Leeds in July 2004. He scored 19 goals for Boro in the 2006-2007 campaign.
Meanwhile, Newcastle also want out-of-contract Bolton defender Tal Ben Haim.
Allardyce, who resigned as Trotters manager in April, told the Newcastle website: "Yes, I'm interested in Tal Ben Haim. He is a free agent and is hopefully available."