The 45-year-old replaces former England team-mate Andrew Strauss in the role, with the latter having stepped down in October in order to spend more time with his family.
Giles, who will officially start in January ahead of England's tour of the Caribbean, leaves a similar role at Warwickshire and his appointment means he has represented England as a player, coach and now an administrator.
Giles said: "I am delighted to be joining the ECB and shaping the future of England cricket throughout the men's game.
"I am very grateful for the opportunity and excited about working with some talented people. The legacy left by Andrew Strauss has put the performance programme in a stable place.
"It is fundamental that I facilitate the great work currently being carried out, meet our objectives and help our sport achieve great things in the coming years both domestically and internationally."
The former left-arm spinner won 54 Test caps for England, including famously lifting the Ashes urn in 2005, while he played in 62 one-day internationals.
Giles coached England's limited-overs side for 18 months, reaching the 2013 Champions Trophy final, while he has also enjoyed success as a coach with Warwickshire and Lancashire.
A number of candidates had been mentioned for the ECB post, including Strauss' predecessor Andy Flower, but Giles got the nod following a month-long formal recruitment process.
ECB chief executive officer Tom Harrison said: "We were fortunate throughout this process to interview some of the most talented and respected people in the game.
"Ashley was the standout candidate amongst a very strong field. He will bring a fresh perspective to the role and build on the excellent work carried out by Andrew Strauss over the past three and a half years."
