He was the leader of the prominent anti-Vietnam War group Seattle Liberation Front ("Seattle Seven"). He was in favor of the Gulf War in 1991. 
Lerner, a rabbi in the Aleph Alliance for Jewish Renewal, promotes the concept of Jewish Renewal, a small Jewish movement which he describes as "positive Judaism", rejecting what he considers to be ethnocentric interpretations of the Torah. His publications promote religious pluralism and left-wing or liberal approaches to political problems. He has, for example, been outspoken against attacks on immigrant communities in the United States, and has attempted to build bridges with Muslim leaders around such issues.
Lerner's approaches have resulted in challenges to his religious, as well as political, credentials. Lerner identifies himself as a duly ordained rabbi, although many of his critics dispute that claim on grounds that he was given a private rabbinic ordination by a beit din consisting of three "Jewish Renewal" rabbis, whose ordinations are recognized only by those within the Jewish Renewal community and Reconstructionist Judaism, the smallest of American Judaism's major congregational bodies.
Orthodox Judaism, the Reform movement's Central Conference of American Rabbis, and the Conservative movement's Rabbinical Assembly typically consider such an ordination invalid. Although that process, known as semicha, was common in the past after years of independent study, it is much less frequent in the United States these days. To pursue the structured rabbinic training seminary or institution background is more typically the norm. Lerner was accepted into the Jewish Theological Seminary's formal rabbinic program, but declined to pursue it in favor of years of study under private tutelage in a variety of fields. These included Jewish mysticism with the Hasidic rebbe, Zalman Schachter-Shalomi, who had been introduced to Lerner by Rabbi Abraham Joshua Heschel.
Lerner considers himself a Zionist, in that he believes in a Jewish homeland in Israel. Lerner strongly objected to Israel's occupation of the Gaza Strip, and continues to object to its occupation of the West Bank. He supports the adoption of the Geneva Accords as a basis for an independent Palestinian state.
Lerner has had run-ins with left-wing opponents of Israel. Recently, Lerner accused the anti-war group International ANSWER of anti-Semitism, claiming that their decision to bar him from speaking at their rallies against the 2003 invasion of Iraq, was due to his outspoken support for the continued existence of Israel. That said, Lerner spoke at a September 2005 anti-war rally in Washington, DC sponsored by ANSWER.
Lerner has signed the 911 Truth Statement  calling for new investigations of unexplained aspects of the 9/11 events, including the failure of US intelligence to act on warnings of upcoming attacks, the breakdown of military air defense, and the nature of the investigations.
Lerner has also signed the call of the "antifascist" group The World Can't Wait -- Drive Out the Bush Regime.  The statement condemns the Iraq war, torture, the abrogation of habeas corpus, theocracy, the suppression of science, the attacks on abortion rights, and "a culture of greed, bigotry, intolerance and ignorance." It advocates resistance to, and repudiation of, the Bush agenda.
He recently wrote The Left Hand of God. He appeared on C-SPAN to discuss the book on March 5, 2006. He appeared on NBC's Meet the Press with Tim Russert as one of a panel of various religious leaders on April 16, 2006. He, is also the co-founder of the Network of Spiritual Progressives.