It is understood that Alan Kelly, the former environment minister, was unable to get a seconder — meaning he will not be able to contend for the leadership, leaving the way open for Mr Howlin.
Three Labour TDs had put themselves into the mix for the party leadership ahead of today’s deadline.
As well as Mr Howlin and the deputy leader, Mr Kelly, Seán Sherlock had also voiced an interest in taking over as head of the party.
Mr Kelly said members should be allowed to vote on the leadership, while Mr Howlin refused to comment on whether he would take part in such a contest.
The parliamentary party had a number of meetings this week to discuss the leadership. Members would not confirm if any of those wishing to run obtained a seconder to back their nominations for leader.
Under the party’s constitution, Labour has until noon to nominate candidates.
Mr Kelly, who has made his ambitions for leadership very clear, pushed for a ballot of all members of the party: “I believe contest is healthy, but whether one will emanate or not, that’s really a matter for internal discussion.
“Fundamentally we are all here because of the members and supporters who helps us, ultimately any decision that is to come must reflect the members.”
Mr Howlin refused to state whether he would even take part in such a contest if it were to happen: “I am participating in the internal discussions first.”
He said his own objective was to do “the best for the party”.
“We are absolutely determined as a body to rebuild our party, to reconnect with people who vote for us and who think like us, who don’t vote for us yet,” said Mr Howlin.
Meanwhile, Cork East TD Mr Sherlock did not rule himself out of the running to lead the party.