Alyth has appointed a final-year rabbinic student at London's Leo Baeck College as the third member of its rabbinic team.
Hannah Kingston - who is due to graduate from the five-year rabbinic training scheme in summer - will join the Reform synagogue in Golders Green next September.
Shul chair Noeleen Cohen said Ms Kingston " will have a specific role building relationships and programming to respond to the needs of the many young families who make Alyth their home".
Rabbi Josh Levy said he and his Alyth colleague Rabbi Mark Goldsmith were "hugely excited" at the appointment, "part of exciting plans for the future which also include the ambitious development of our building".
Other growing Reform congregations are hoping to add to their rabbinic staff. Finchley Reform is on the lookout for a rabbi to join a ministerial team already comprising Rabbi Miriam Berger, cantor Zoe Jacobs, Rabbi Howard Cooper, director of spiritual development, and Rabbi Shulamit Ambalu as education director.
"Growing from 500 to 825 families leaves structures feeling pulled in every direction," Rabbi Berger said. "We want to retain our small shul identity but have the capacity to keep relationships strong for our growing community.
"We all have very different styles. It means people can find their own member of clergy within their community. I hope our new rabbi will bring another flavour."
When Rabbi Paul Freedman came to Radlett Reform Synagogue, he was the lone minister. But despite the addition of Rabbi Celia Surget, the shul was "clergy-lite". Radlett, he said, was "the third largest Reform synagogue if you count children, with 2,300 souls. Half of our members are under 21."A third rabbi would enable the team to "get ahead of the game in serving the needs of our congregants".