Confirmation of the date emerged after discussions this morning between the legal team for Ms Philips' parents, Sean and Norma, and the Louth coroner.
The inquest into the death of Garda Tony Golden will proceed as scheduled next Monday at Dundalk courthouse.
The legal team had stated they were seeking an adjournment of the inquest on Monday based on the understanding that Mackin's inquest was also going to be held on the same day.
Mackin shot dead unarmed Garda Golden, a father of three children, and seriously injured Ms Philips at the couple’s home in Omeath, Co Louth, on 11 October 2015. Mackin turned the gun on himself afterwards.
Gda Golden was accompanying Ms Philips' to her home to collect her belongings after she had been attacked by her partner, Mackin.
John Rogers SC for Ms Philips’ parents agreed with the coroner that Gda Golden's inquest should go ahead as planned on Monday.
Sean Philips said: "We don't want to cause any more stress to the Golden family and we don't want to obstruct the Golden family in any way."
He said their issues concerning the inquests would now only be relating to Mackin's inquest which will be held on 29 May at Dundalk.
His legal team has told the coroner that various articles of the European Convention of Human Rights will be engaged at the hearing and that the inquest will have to be “compliant” with those provisions.
Gsoc has “many issues” with a Garda report relating to the shooting dead of Garda Tony Golden and serious injury of Siobhan Philips in October 2015.
The Garda review, published at the end of March, examined events leading up to the shooting at Omeath, Co Louth, and interactions between the gunman Adrian Crevan Mackin, who was Ms Philips’ abusive partner and a dissident republican, and gardaí.
Garda Golden, a 36-year-old father of three, accompanied Ms Philips, 24, back to her home on October 11 when Mackin opened fire on them before turning the weapon on himself, taking his own life.
Gsoc is conducting a public interest inquiry into the entire circumstances, a probe it set up in April 2017.
Following the publication of the Garda reports, Gsoc wrote to the family saying they had “many issues” with the review, but declined to specify what they were.
The investigating officer did say that the report was incorrect in referring to the Gsoc probe as a criminal investigation, pointing out it was a non-criminal inquiry, although this did not preclude the possibility of a criminal one arising.
Ms Philips’ father Sean and stepmother Norma have called for a public inquiry into the matter and, separately, are suing the State.
Their legal team is also seeking an adjournment, for six months, to the inquests, scheduled to take place in Dundalk next Monday. The lawyers have asked for time to study depositions and post-mortems.
They said that various articles of the European Convention of Human Rights will be engaged at the hearing and that the inquest had to be “compliant” with those provisions.