It follows a hugely successful spell that saw Shiels and the players make history by qualifying for a first major tournament.
Northern Ireland reach the Euro 2022 finals in England last summer. Although they were knocked out at the group stage, it was considered a watershed moment for the national team and women's football in the country.
Shiels is set to leave despite having one year remaining on his contract. The Irish FA did not comment when contacted by Sky Sports News.