A photo of the 19-year-old signing his five-year contract with the club were shared by journalist Tim Žaja on Twitter just before 8pm this evening, not long after his sister Blanka's Instagram story seemed to confirm that he was now an Everton player.
Vlašić, who will wear the No.27 jersey, impressed during the Croatian side's two-legged Europa League playoff tie with the Toffees this month and has become the latest signing to arrive at Finch Farm this summer.
A former target of Arsenal and Chelsea, Vlašić was reported to have turned down a move to the Premier League last year to remain in Croatia and support Blanka's preparations for the 2016 Olympic Games.
He was apparently watched closely by AC Milan more recently but Everton have beaten off the competition to sign him. His participation in the Europa League group stages won't cup-tie him for the group stages of the competition and beyond.
An attacking midfielder who can operate across the forward line, Vlašić has made 87 league appearances and scored 11 goals for Hajduk since breaking into their team three years ago.
He was recently won his first cap for his country's senior team but is on duty with Croatia's U21s during the current international break from which he was given permission to take time off yesterday to conclude a medical and personal terms with Everton.
Under the terms of the deal, Hajduk would be due a further £925,000 (at current exchange rates) if certain appearance-related clauses are met, plus 10% of any sell-on fee for Vlašić.
“Nikola is one of those players who can play a big part in Everton's future and in what we want to achieve as a club,” Ronald Koeman said of the new acquisition.
Vlašić, meanwhile, expressed his delight at finalising the move.
“When there is a manager like Ronald Koeman who wants you, there is no need to talk about it much,” he said.
“I wanted to come here because of the manager, because of the big players, because of the reputation of the club. It is the opportunity of a lifetime.
“I played a lot of games for Hajduk Split but the Premier League is something else. I am very excited about the opportunity to play for this big club.
“The Premier League is the best league in the world and this is one of the top clubs in England. It is such a big honour for me to be here.”