The 41-year-old had been due to work a 12-month notice period with West Brom, but will instead be available on a one-day-a-week consultancy basis until the summer.
Ashworth's replacement as Albion's sporting and technical director, Richard Garlick, was appointed in January.
Albion chairman Jeremy Peace paid tribute to the achievements of Ashworth during his nine years at The Hawthorns.
He said: "Dan has worked tirelessly for this football club for the past nine years and leaves with our best wishes.
"He has remained fully committed to his club responsibilities since it was announced last September he would be leaving, for which I would like to thank him.
"The handover process with Richard has gone extremely well, which has enabled us to agree to an early departure date with the FA for Dan, and we now look forward to Richard building on the solid foundations laid by Dan."
Ashworth, who will be based at the National Football Centre at St George's Park, is leaving West Brom with mixed emotions.
He said: "I have had nine fantastic years here and I just want to say a big thank you to everyone connected with the football club - the staff, players and supporters.
"As with any football-related job, there have been some lows but we have managed to bounce back from them all and there have undoubtedly been far more highs.
"With the January transfer window now closed, the team having already amassed 40 points and Richard very much hands on in his new role, we all agreed this would be an appropriate time for me to move on.
"But I will continue to help the club in any way possible in my consultancy capacity."
Ashworth added: "It was a really tough decision for me to leave but the FA presented me with a wonderful opportunity which I could not turn down.
"I've worked closely with Richard for the past two and a half years and he has all the attributes to be a fantastic sporting and technical director.
"I have every confidence he will make a real success of the role."
Fair enough. Good luck Dan. We wouldn't be where we are today without him.- Fuzzy_Dunlop