Former England captain Strauss stepped down from his position in October to support his wife Ruth in her fight against cancer.
Giles played 54 tests for England and later worked as a national selector from 2008-2014.
"I am delighted to be joining the ECB and shaping the future of England cricket throughout the men's game," the 45-year-old said in a statement.
"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 marks a comeback to the ECB set-up for Giles, after he was sacked as England's one-day international coach in 2014.
Giles' credentials will be tested over the next 12 months as England host the 50-over World Cup and the Ashes series against Australia.
The appointment follows a month-long recruitment process led by ECB chief executive Tom Harrison.
"Ashley was the standout candidate amongst a very strong field," Harrison said.
"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."
(Reporting by Hardik Vyas in Bengaluru; Editing by Toby Davis)
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