Singh is learnt to have arrived at the decision after a late night meeting Thursday with RSS number two Bhaiyyaji Joshi at the RSS office Keshav Kunj in the capital.
However, efforts were still being made to soften L K Advani and party leaders were banking on former BJP president Nitin Gadkari to convince him. Gadkari met L K Advani late Thursday night, sources said.
Singhs office said the parliamentary board meeting had been called at 5 pm Friday. But L K Advanis office said it had not received any such communication.
Singh, they said, apprised the RSS bosses about his discussions within the party following two days of talks between the BJP and the RSS that ended Monday. Singh had held talks with L K Advani and separately with senior leader Murli Manohar Joshi on Wednesday. On Thursday, he met leader of opposition in the Lok Sabha Sushma Swaraj.
Advani, Joshi and Swaraj are against Narendra Modi being named the partys PM candidate before the crucial assembly elections in Chhattisgarh, Madhya Pradesh, Rajasthan and Delhi later this year.
Singhs talks with these leaders were an attempt to show the RSS leadership that he had tried his best to get them to back the announcement and to avoid being accused of working unilaterally, an allegation that was made after he declared Narendra Modi the partys chief campaigner for the 2014 Lok Sabha polls at the partys national executive meeting in Goa in June.
In another bid to demonstrate that all efforts were made to placate Advani, whose objections are considered to be the most assertive, Singh deputed BJP leaders Venkaiah Naidu, Ananth Kumar, Murlidhar Rao and Shahnawaz Hussain to meet L K Advani Thursday and get him to relent.
RSS ideologue S Gurumurthy, who was instrumental in convincing L K Advani to stay on after the Goa episode, also met L K Advani Thursday.
Sources said that all leaders who met L K Advani felt that unlike in June when he skipped the partys national executive meeting, the former deputy prime minister will attend Fridays parliamentary board meeting.
Given his opposition to the timing of Narendra Modi being announced as the PM candidate, sources said the Friday meeting could see a showdown between L K Advani and Narendra Modis supporters.
L K Advani had been forthright in voicing his objections to Modi being named before the Assembly polls even during his meetings with RSS chief Mohan Bhagwat and Bhaiyyaji Joshi earlier this month.
There was very little option but to call the parliamentary board meeting. Not calling a meeting before the announcement would have sent a very wrong message about the lack of unity within the party, a party source said. At the same time, the BJP leadership was cagey about holding a meeting because any boycott would have also sent a wrong message.
L K Advani and Sushma Swaraj favouring a parliamentary board meeting paved the way for convening it, sources said.