“We will challenge the [Netanyahu] government until we reclaim the leadership [of the country],” said Isaac Herzog, the Labor Party’s new chairman in his acceptance speech Friday morning, hours after his victory over outgoing chairwoman Shelly Yachimovich was announced.

“Today we started a path that will lead to the return of the Labor Party to the helm of the country, and we will win. The work has begun to return [this party] to its rightful place,” Herzog said at the festive press conference Friday in Tel Aviv.

Herzog thanked his supporters and called on all Labor voters and MKs to come together under his leadership. “I will be your voice [in the Knesset] and I will not disappoint,” he promised.

He also spoke about Israel’s many challenges — including the Iranian threat, the recent clash with the United States over the emerging deal with Tehran in Geneva, his perception that Prime Minister Netanyahu fails to understand the importance of peace with the Palestinians, and the country’s many social-economic issues such as what he termed rising unemployment, unfair housing costs, and signs of a recession.

Asked directly if he would join the ruling coalition, Herzog said: “I will serve as opposition leader. And I will meet with the prime minister when relevant… I have said before that if he makes a clear, daring step toward peace, I would be there. I stand by what I said.”

“We just got elected. This isn’t the time [to discuss a coalition]. Will all of you stop talking about it?” his spokeswoman told The Times of Israel Friday.

The question of whether Labor might join the government will be an early issue for the new leader. Yachimovich had refused the prime minister’s pleas to join him after January’s elections, promising instead to provide a Labor “safety net” from outside the coalition to ensure support for any peace moves with the Palestinians.

Earlier Friday, Herzog defeated Yachimovich by 16 percent — some 3,000 votes — for the leadership of the long-embattled party.

With over 90% of the votes counted by 9:00 a.m., Yachimovich called Herzog early Friday morning to congratulate him on his win of 58%-42%. The two agreed to work together to advance the interests of the party.

“Shelly Yachimovich called me a moment ago and congratulated me on being elected chairman of the Labor Party,” Herzog wrote on his Facebook page. “She said she was committed to the success of the party, under my leadership, and to its return to power [in national politics]. I thanked her sincerely and reiterated that I see in her an important partner.

“Friends, this is the beginning of a new journey,” he went on. “Today, we’re starting on a path to change the face of this country… We have a lot of work ahead of us.” Herzog convened a press conference at 10:30 a.m. local time to formally speak about his victory.

Yachimovich also took to Facebook to comment on the results.

“I called [Isaac] ‘Bougie’ Herzog to wish him success. I told him… it was a fair race and I would cooperate and help him strengthen the party as an alternative to the right-wing Netanyahu government,” she wrote.

Yesh Atid leader Yair Lapid was the first to applaud the new chairman on the social media site, saying: “Big congratulations to ‘Bougie’ Herzog. We have been friends for many years and I’m very happy for him on his victory.”

Hatnua chairwoman Tzipi Livni said she sees renewed importance for the peace process in Herzog’s victory.

“I believe that ‘Bougie’ really believes and is really committed to a [peace] agreement and I hope he will help change the [expected] script for everyone here. The peace process needs real support. In short, congratulations and, together, we can block the extremists,” she wrote.

Livni has in the past strongly encouraged the Labor Party to join the coalition to advance the peace process.

Yisrael Beytenu leader Avigdor Liberman congratulated Herzog, wryly wishing him “many years as head of the opposition.”

President Shimon Peres, a Labor Party stalwart, told Herzog that he now carries a great responsibility on his shoulders. “You must serve the people and the country in the best way possible. I congratulate you and wish you great success,” he told Herzog.

Slightly over half of eligible Labor Party primary voters cast ballots in the party’s leadership primaries by the time polls closed at 10 p.m. Thursday, already leading to worries in Yachimovich’s camp that the low turnout could unseat her.

“Voting percentages are quite low; they are not good for us,” Yachimovich said in an interview with Channel 2 News Thursday evening.

According to a text message sent out by Labor Party officials Thursday, a total of 52.7% of eligible party members had voted in the primaries.

Herzog, who was also interviewed by Channel 2, criticized Yachimovich for leading the party with too firm a hand, and said he believed “in collaborative leadership.”

“The nation of Israel has had enough one-time leaders,” he said, a reference to Labor’s 18-year streak in which none of the party’s incumbents have won reelection. The country, Herzog added, “wants someone who will get the job done.”

“I will get the job done,” Herzog concluded.

Some 55,000 members of Israel’s Labor Party were eligible to vote in the hotly contested party primary.

Polls opened at 10 a.m. at 79 voting locations around the country, an increase from 68 sites during the last primaries in 2011. Party members were allowed to cast their ballots at any of the stations, regardless of their place of residency.

Last week, a poll commissioned by Channel 2 political anchor Nissim Mishal showed Yachimovich holding a comfortable lead over Herzog among Labor voters, 64.4 percent to 35.6 percent.

But the Herzog campaign pointed to a second poll commissioned by Mishal, which asked the same question among the general public. That survey showed that most Israelis would prefer to see Herzog head the Labor Party rather than Yachimovich, by 54% to 46%. That gap suggests that Labor might do better at the ballot box under Herzog, according to his supporters.

Once a powerhouse in Israeli politics and the flagship of the Israeli center-left, Labor has seen its influence wane in recent years. The party once reliably won more than 30 Knesset seats, and as many as 44 in the 1992 election that brought Yitzhak Rabin to power on a peace platform, but dropped to just 13 seats in 2009 under the leadership of former prime minister Ehud Barak. Yachimovich led the party in the latest elections in January, and garnered a disappointing 15 seats, just two more than the party’s worst-ever electoral showing.

If Yachimovich had retained the leadership Thursday, it would have marked the first time a Labor leader was reelected to a consecutive term since Peres won reelection as party leader in 1988. Likud, in all its incarnations, on the other side of the political map, has had just four leaders in the 65 years of Israel’s existence; Labor has seen eight in 21 years.

That instability, Yachimovich’s supporters have said, has been a key factor in the party’s lackluster showing in recent years. Labor has held the premiership for only two years in the past 17.

“We’re going to make history,” Yachimovich’s spokeswoman Bar Peled told The Times of Israel in October. “The Labor Party will reelect a chairperson for the first time in a long time.”

Yachimovich had the public support of seven Labor MKs — Avishay Braverman, Michal Biran, Moshe Mizrahi, Mickey Rosenthal, Itzik Shmuli, Nachman Shai and Stav Shaffir — and the tacit support of more. Some MKs, such as party secretary-general Hilik Bar, are refusing to side with a candidate due to their roles in the party’s institutions, but were identified in the past as Yachimovich supporters.

Herzog, a former welfare minister and son of former president Chaim Herzog, garnered the support of fewer MKs, including Eitan Cabel, Merav Michaeli and Erel Margalit.