Galon, Meretz's incumbent leader, cited desire by Meretz activists for a new chairman. "From conversations I've had all over the country with registered voters in recent weeks, I've realized they wanted a new leadership," she said.
Gilon, meanwhile, said a medical issue led him to withdraw from the race after spending the last few days in the hospital.
Zehava Galon resigned from the Knesset last November in an effort to lead a change in her party, seeking to take the power to select Meretz's chairman and Knesset list from the party delegates and give it to its registered voters in primary elections.
Thanks to her campaign, the party grew by 70 percent, with 31,000 new registered voters joining its ranks.
"Opening Meretz's doors has been a massive success, and I don't regret it for a moment. My entire political life, I've fought for my principles and values. I would've done it all again, even if I had known the personal price I'd have to pay," Galon said in a statement.
She said she has been a member of Meretz "from the day I was given the voting right. To me a party is a tool for change, not a work arrangement. I've criticized politicians for holding onto their seats quite a few times, and today I have the opportunity not just to demand but also to live up to my principles and send out a message: elected public representatives are messengers for the public who need to fight for the future and not for their jobs. I'm proud of the fact I had the privilege to lead the Israeli Left, and I'm happy to see Meretz opening its doors. I know I am leaving a stronger and more established party to my successor than the one I received."
Galon went on to lament the fact that "The advocates of peace, human rights, equality and justice are going through a difficult time not only in Israel, but all over the world. We see massive waves of fanaticism, radicalization, racism, hatred, incitement and corruption hitting Israel, Europe and the United States. Meretz is an ideological lighthouse, which remains steadfast in the face of a tsunami, and the difficult trials have only just begun. But today, this is a lighthouse with an army of 31,000 people. I am retiring, but remain recruited."
In his own statement, Ilan Gilon explained he had "a medical event, which limits my ability to continue the campaign as I would've wanted to. I will continue to serve the public as the head of Meretz's Knesset faction and continue to promote the values I was sent to the Knesset to advance."
"Our mission, of creating a different left-wing and a different Israel, hasn't changed," he wrote in a Facebook post. "In the coming days, the Reds, the biggest and most significant political group in socialist Zionism, will convene, and we will make decisions on how to continue on our path together. We still have a long way to go."
Four candidates left in the race
Only four candidates remain in the running for the party's leadership: Sitting MK Tamar Zandberg, Peace Now director Avi Buskila, Avi Dabush and Imri Kalmann.
Internal polls conducted by all of the candidates have shown Galon had low chances of winning. She is expected to give her support to Buskila.
In the wake of Galon and Gilon dropping out of the race, Zandberg's chances of winning the March 22 primary elections have increased. However, if none of the candidates receives at least 40 percent, a second round will be held.
"Zehava is a brave and groundbreaking leader, who is on the same level as Shulamit Aloni and Yossi Sarid," Zandberg said after Galon's announcement. "She led Meretz and the Israeli left to significant achievements during a time of difficult turmoil. Galon has shown courage and responsibility in pushing for the opening of the ranks in Meretz. This is the end of one chapter in Galon's magnificent career, and I am convinced she will continue being part of Meretz's leadership in her new chapter."
Zandberg described Gilon as the "beating heart of the Left."
"First and foremost, I wish him good health and a quick return to the forefront of the social struggles Israel so desperately needs," she added.
Buskila also praised Galon, saying she is "one of the most impressive leaders of the Left we've had here. From day one, she has always spoken with a clear voice against the occupation and in favor of social justice, she dealt with rights issues that no one else would even touch and promoted civil issues. Galon will remain a central part of Meretz, because we can't afford losing people like her."