Singh will chair a meeting of the BJP Legislature Party which will elect its leader, who will be the Chief Minister.
Singh was appointed as an observer for Maharashtra after BJP emerged as the single largest party in the Assembly polls securing 122 seats out of a total of 288.
Sources said the BJP is in back channel talks with Shiv Sena over government formation and efforts are being made to settle the differences with its oldest ally with whom it snapped ties ahead of polls.
Prime Minister Narendra Modi has called a meeting of all NDA MPs at his residence tomorrow which Shiv Sena members will also attend.
Modi is in Mumbai today to inaugurate a private hospital there. It was, however, not clear whether he would have any political meeting during his visit.