Rabbi Naftali Brawer has announced his resignation from Borehamwood and Elstree Synagogue to take on a new public role.
The American-born minister, who will leave in August after four years with the congregation, is to lead a foundation dedicated to promoting spirituality at work.
He told members in a letter that he "certainly did not plan to do this sort of thing when I became a rabbi, and yet after serving in that capacity for close to 20 years, I have been presented with an extraordinary opportunity to positively influence wider society".
Borehamwood chairman Anthony Arnold said he would have liked Rabbi Brawer and his wife Dina - a Jewish educator in her own right - to continue leading the community. But an interim minister would be appointed until a permanent successor as senior rabbi could be found.
Rabbi Brawer had been tipped as a possible contender for the Chief Rabbinate after the retirement of Lord Sacks in 2013, although he is thought by some to be too modern in his views for the London Beth Din.
He joined the United Synagogue as rabbi of Northwood Synagogue in 1996 before succeeding Rabbi Alan Plancey at Borehamwood. He is the Chief Rabbi's representative on Muslim-Jewish relations and joint vice-chairman of the US rabbinical council.
Acknowledging that some congregants may have been surprised at his decision to move, Rabbi Brawer said he would explain it further in his sermon on Shabbat week.
But in his letter, he revealed he had been headhunted by a "group of global benefactors" to head the foundation in London.
Spirituality in the Workplace is an American movement that began in the 1980s, he explained. His new position would involve helping companies to "construct a framework within which employees can express and develop deeper ideals and values.
"These ideals and values include ethical business practices, corporate responsibility, respect for diversity and the environment, the centrality of family and community, balance and harmony in one's personal and professional life and using wealth to improve the lives of others."
His departure will leave the US having to rebuild its spiritual leadership for the expanding Hertfordshire communities. Rabbi Leo Dee is not due to join Radlett as its new rabbi until spring. Shenley is yet to name a successor to Rabbi Natan Levy, who is making aliyah.