Blackburn are currently 22nd in the table and are outside of safety on goal difference.
They have been without a manager since Valerien Ismael left his role on 2 February, with Johnson taking interim charge.
O’Neill, 56, had a similar agreement with Stoke City when his first tenure came to a close in 2020, where he would combine duties with club and country.
However, the Covid-19 pandemic delayed the Euro 2020 play-offs and O’Neill left his role before those games took place.
He returned to the international dug out in 2022 and signed a contract until after the Euro 2028 campaign.
Northern Ireland are aiming to qualify for a first World Cup in 40 years, and a first major tournament since O’Neill guided his country to the Euro 2016 finals in his first spell.
He was at the Nations League draw on Thursday, where NI drew Hungary, Ukraine and Georgia, but did not speak to the media in Brussels.