Yitzhak Herzog and Tzipi Livni
Yitzhak Herzog and Tzipi LivniMiriam Alster/Flash 90

Hatnua Chairman Tzipi Livni will officially join Yitzhak Herzog's Labor Party, Livni announced Wednesday - forming a joint list which could make a leftist bloc a formidable force in the upcoming elections. 

A press conference on the joint list will be held at 8:00 pm Wednesday to reveal more details of the pact, which has been brewing for weeks. 

On Friday it was reported that Herzog and Yesh Atid chairman Yair Lapid are competing to bring Livni into their parties in a bid to become the largest in the "center-left" bloc as it is being referred to. That report said that Livni had been leaning towards Herzog.

A poll released Monday found that a pact between Labor and Hatnua could see it win the most seats in the 20th Knesset.

According to the poll, which surveyed some 500 respondents, the Labor-Hatnua pact would win 23 Knesset seats, edging out Likud's 21. Jewish Home would come third with 18 seat, while all of the "centrist" parties - including Moshe Kahlon's new party, Avigdor Liberman's shifting Yisrael Beytenu, and Yesh Atid - would gain nine seats each.

United Torah Judaism would win eight seats, Shas would win seven, Meretz would win six and the Arab parties (United Arab List, Balad, and Hadash) would win 10 seats altogether.

Livni has said recently that she is "ready to be Prime Minister" - an option only possible with a join list, as recent polls have indicated that Hatnua would not make the minimum vote threshold for the Knesset without the deal.