Cleveland Dodd, 16, was found unresponsive in his cell in a troubled youth wing at a high-security adult prison in the early hours of October 12.
He was taken to hospital in a critical condition, where he later died, causing outrage and grief in the community.
About 500 mourners were expected at the boy's funeral on Friday afternoon in the remote town of Meekatharra, about 750km northeast of Perth.
The service, originally scheduled for 8am, was postponed earlier in the day when Cleveland's father Wayne Gentle told his family authorities would not allow him to attend.
Social justice advocate Gerry Georgatos said he was involved in a "crisis meeting" with police and Corrective Services and they reversed their decision after reassessing security concerns.
"(Mr Gentle) is being flown in by four o'clock and the funeral will go ahead," he told AAP.
Supporters of Cleveland Dodd marched rallied in Perth after his death. (Aaron Bunch/AAP PHOTOS)
Mr Georgatos said about 200 of Cleveland's family members had peacefully protested outside the Meekathara police station after the funeral was delayed.
He was scathing of authorities over the earlier decision, saying "to do this at the last minute created a lot of chaos in the community, upset and unnecessary trauma".
The Department of Justice issued two statements on the matter, with the first saying the Corrective Services Commissioner had been "guided by safety and security concerns" when it declined Mr Gentle's request to attend his son's funeral.
"Today the family, WA Police and Corrective Services have come to a new agreement in relation to security and we can now support the family's request," the second read.
"It was always the Commissioner for Corrective Services' desire to facilitate the father's attendance at the funeral if it could be done safely."
WA Greens MP Brad Pettitt was also lobbied on behalf of Cleveland's family, and contacted Police and Corrective Services Minister Paul Papalia to have him intervene.
"After everything that has happened, I am shocked at the lack of humanity that continues to be shown by this government and by the Department of Corrective Services towards Cleveland Dodd's family," he said before the decision was reversed.
