Emery, 46, joined Arsenal after completing a two-year spell at Paris Saint-Germain, where he landed three titles including the French Ligue 1, reports Xinhua news agency.
He had previously spent three seasons with Sevilla, leading them to an unprecedented three consecutive Europa League titles.
"I'm excited about what we can do together and I look forward to giving everyone who loves Arsenal some special moments and memories," Emery said.
Arsenal's chief executive Ivan Gazidis said Unai had an outstanding track record of success throughout his career.
Emery started his coaching career at Lorca Deportiva in 2005 after playing mostly in the Spanish second division. He went on to coach Almeria, Valencia and Spartak Moscow before joining Sevilla and Paris Saint-Germain.
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