Sinn Féin is to attend a PSNI graduation ceremony for the first time on Friday, BBC News NI has learnt.
First Minister Michelle O'Neill and the party's policing board member Gerry Kelly have accepted an invitation to attend the event at Garnerville.
It will be the first time Sinn Féin politicians have attended a passing out ceremony since the PSNI was established 23 years ago.
It is understood Deputy First Minister Emma Little-Pengelly will also attend.
Alliance leader Naomi Long will be at the event in her role as justice minister.
However, Ulster Unionist policing board member Mike Nesbitt has criticised the PSNI Chief Constable Jon Boutcher for his party leader Doug Beattie not being invited.
"By definition, that is not inclusive," he said, highlighting the other three Executive parties would be represented at the ceremony.
Sinn Féin confirmed its party's move in a short statement on Thursday evening.
A spokesperson said: "Tomorrow the PSNI student officer attestation ceremony takes place where a number of new recruits will graduate.
"Michelle O"Neill will be in attendance and will join the ceremony. Sinn Féin Policing Board member Gerry Kelly MLA will also attend".
'Lukewarm' support of PSNI
Sinn Féin has in the past been accused of having a lukewarm approach in its support for the PSNI.
But four years ago Michelle O'Neill and Gerry Kelly attended the launch of a PSNI poster recruitment campaign.
The chief constable at the time, Simon Byrne, described the move as "seismic and historic".
He said he hoped it would have a significant impact on the PSNI's ability to recruit more Catholic officers.
But since then Sinn Féin has turned down invitations to attend PSNI graduation ceremonies.
Liam Kelly of the Police Federation for Northern Ireland, said the attendance of Sinn Féin members would be "a little bit of history" and hoped it would become "the new normal".
"Unfortunately, only a small number of student officers are graduating and that's way below what is urgently required," he added.
"We would like the first minister to realise the dire and parlous state that policing finds itself in and to lead the effort to secure adequate resources and meaningful recruitment."
Last week, the PSNI chief constable Jon Boutcher said a recruitment drive was to be launched after numbers fell by around 1,000 in recent years due to budget pressures.
Meanwhile, DUP MP Gregory Campbell said that it was "better late than never".
He told BBC News NI's Evening Extra: "It is an unequivocal welcome of a step which should have occurred many years ago.
"Hopefully it will lead on to further support to get people from across the community to join the police, and I mean active support, not just a statement."
Analysis: A positive long overdue step
Sinn Féin's decision to end its boycott of PSNI passing out ceremonies is significant.
It marks a turning point in the party's visible support for the PSNI.
A positive, long overdue step coming almost 18 years after Sinn Féin first signed up for policing.
It also plays to Michelle O'Neill's promise to be a First Minister for all.
But will it help to drive up Catholic recruitment beyond the current level of 32 per cent?
Until now Sinn Fein has challenged the PSNI to do more to attract young Catholics.
Is the party now putting its shoulder to that wheel? Time will tell.
But don't expect a full on PSNI parade of new recruits around Garnerville. This will be a low key gathering with around six officers passing out.