The former Everton man has put pen to paper on a four-year deal at The City Ground and arrives following a successful 2015-16 season in which he found the net 11 times for Iraklis in the Greek Super League.
Vellios began his career with Iraklis, making his debut for the club in 2009, and his first goal for his hometown side was a memorable one as he scored a last-minute equaliser against Olympiacos.
His impressive performances attracted attention from a number of clubs around Europe but it was Everton who secured his services in January 2011. He found the net in his second game for the Toffees against Wigan in September of that year before scoring against Chelsea at Stamford Bridge a month later.
Despite being named Everton’s Young Player of the Year in May 2012 and having enjoyed a brief loan spell with Blackpool, Vellios made the move to Belgian side Lierse at the end of the 2013-14 campaign in search of more first-team football.
He made an instant impact once again, scoring a last-minute equaliser away at Standard Liege, but opportunities were at a premium and he spent the second half of the season on loan at Danish side Vestsjaelland where he scored three goals.
A move home to Iraklis last season appeared to provide Vellios with a significant confidence boost and he scored a hat-trick in their 3-0 win over Kalloni in January to add to the winner he netted against Panathinaikos earlier in the campaign.