Ashworth has started in his post as technical director after the club last week agreed a compensation deal with Brighton and Hove Albion, where he had been technical director.
“Newcastle United is an incredible football club, and I’m delighted to be joining at this very exciting time,” said Ashworth.
"Each time I’ve been to St James’s Park in the past, I have been reminded of the club's long history – and the unrivalled passion of its fan base. It is a huge football club with great potential, and I am incredibly positive about what we can collectively achieve. I’m excited to start work immediately, and look forward to being part of a team that is helping the club to grow and achieve long-term success."
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Ashworth – who also had a spell at the Football Association – will oversee the club’s efforts in the summer transfer window.
In a joint statement, the club’s owners said: "On behalf of the board, staff and players, we would like to welcome Dan Ashworth to the Newcastle United family.
"Dan was the ideal person for this hugely important position. He has a strong track record in elite level football, and we are delighted to have him join Newcastle United ahead of the new season."
Head coach Eddie Howe has been keen for the club to appoint a sporting director.
Speaking last season, Howe said: “I’ve been used to working with a sporting director at Bournemouth, so I would encourage that. I believe I can work under any framework, really.”