After rabbinical school, Brenner studied with the Modern Orthodox theologian Rabbi Yitz Greenberg and went on to serve on the faculty of CLAL- The National Jewish Center for Learning and Leadership from 1998 – 2003. At CLAL he authored works on medical ethics with Joseph Fins MD (Chief of the Division of Medical Ethics at Weill Cornell Medical College) and Rabbi Tsvi Blanchard (Embracing Life and Facing Death, A Jewish Guide to Palliative Care, 2002) on spirituality with Rabbi Zalman Schachter-Shalomi, and on a variety of Jewish topics for periodicals including The Forward, Spirituality & Health, Beliefnet, and The Jewish Week.
In 2007, Brenner became the vice president, education of the Birthright Israel Foundation and the founding executive director of Birthright Israel NEXT, an organization dedicated to engaging young adults in Jewish community life. Under his guidance, Birthright Israel NEXT grew to become a national organization with programs that reached over 50,000 young Jewish adults each year. As part of this effort, Brenner launched Next Shabbat, a grassroots program that has sponsored over 20,000 home-hospitality events, brought on HBO Def Poetry Jam artist Vanessa Hidary to direct The Birthright Monologues and worked with Nextbook and Toby Press to develop the anthology “What We Brought Back.” In 2009, he was named by Newsweek Magazine as one of America’s fifty most influential rabbis.