The Ghanaian's loan deal was confirmed in a release on Everton's website:
"I'm very happy to be joining Everton because it's a great club, which likes to play football, and it's a great pleasure to be here," Atsu told evertontv. "Playing in the Premier League has always been a dream for me and I have achieved that dream.
"This is the biggest level for me to play at. I know that it's a very competitive league and I believe with hard work we're going to be successful this season."
Everton also shared the first image of Atsu with the club's shirt on Twitter:
Roberto Martinez also spoke his latest addition in the release:
Roberto Martinez had previously expressed his desire to add a wide man to his squad and the Toffees chief said: "He's a player who fits in with the culture and the way we want to play. He's a very gifted technical footballer and he's got the right personality and character to fit in with the group, which is vital.
"He will excite fans because he brings something completely different and a different way of playing to what we've got in the squad.
"He's a left-footed player who loves taking people on and he's got a really good understanding of the game for such a young man.
"He also brings extra competition in a position in which we felt we needed a player full of desire and hunger, who really wants to make things happen in the final third of the pitch."
Atsu's nomadic career sees him move away from the Blues on a temporary basis for the second time. He impressed during a loan spell with Eredivisie outfit Vitesse last season, scoring five goals and providing six assists in 28 appearances, recorded by WhoScored.com.
The 21-year-old originally moved to Porto after spending time with Feyenoord's Ghanaian-founded branch and has also completed a loan spell in Portugal with Rio Ave. Everton will be the attacking midfielder's fifth port of call since 2011, raising questions as to whether he will ever break into Jose Mourinho's first-team plans.
Casual viewers may have first encountered Atsu at the 2014 World Cup, where he provided wide support for Akwasi Appiah's disappointing team. He performed well in a side that was plagued with disciplinary problems, highlighted by Kevin-Prince Boateng and Sulley Muntari being sent home from the competition.
Atsu offered pace, skill and ambition from the flank, racking up three shots and 1.3 successful crosses per match, noted by WhoScored.com. He represents a smart piece of business from Roberto Martinez, who may be feeling the cost after dropping £28 million on Lukaku, per Sky Sports.
The Belgian behemoth proved to be one of three extremely successful loans during his initial stay at Goodison Park last year. Martinez mobilised minimal funds to further bulk his squad with Gareth Barry and Gerard Deulofeu.
Will Christian Atsu outscore Gerard Deulofeu, who scored three goals during his loan spell with Everton?
With Lukaku and Barry now added permanently, alongside midfielder Muhamed Besic, Martinez will be hopeful of Atsu's arrival filling the void left by Barcelona's flying forward. There is little indication Deulofeu will appear on Merseyside next season after the 20-year-old confirmed he will fight for a first-team place at the Camp Nou.
Even so, he underlined the type of experiences Atsu can expect while under Martinez's tutelage. "I learned a lot, but I still think I deserved to play more … But it was a good experience," said Deulofeu, via Barca's official website. "I have improved in terms of fitness and defending, although my mid-season injury had an impact."
Atsu possesses the type of pace that should see him regularly hit the byline for Everton. He will be expected to contribute accurate service toward Lukaku, who'll patrol the middle looking to latch onto crosses. While Atsu isn't much of a defensive entity, his energy ensures he can be a key vessel during Everton's counterattacks.
The deal is typical Martinez; efficient, well-priced and positive for all parties involved. Everton supporters will hope the Spanish manager's judgement is as meticulous last year, where he significantly improved the side's output through loan signings.
Atsu has it all to prove in the Premier League, but there's no better stage to impress than in front of the Toffees faithful.