'leading partner' is correct and usable in written English.
It is used to describe someone who excels in a particular role in a professional business relationship. For example, "Jane is our leading partner in the development of the new software product."
When leading partner's unsupported suit, lead high from a doubleton, low from a tripleton (unless you have touching honors or, if it is a suit contract, ace-third).
Germany is China's most important trading partner in Europe and China is Germany's leading partner in Asia.
With its relative prosperity and its melding of democratic and Islamic values, Turkey was seen as the leading partner.
Britain, the leading partner, has insisted on retaining "operational sovereignty"—the ability to maintain and upgrade the plane on its own in future.
Of the hundred-or-so program-packaging outfits, few are better known to the public than Talent Associates, Ltd. whose production chief & leading partner is David Susskind Talent Associates specialize in live drama.
ONWARD & UPWARD WITH THE ARTS about David Susskind, the leading partner of Talent Associates, Ltd. the largest producer of live TV programs, & his struggle to get sponsors & air time for next season's shows.
Its leading partners are Richard Mayo, an appointee of Gov. Pete Wilson whose duties included selling state-owned property; Grover L. McKean, a former state deputy treasurer; and Chandra R. Patel, whose biography lists real estate interests in Irvine, Mumbai and New York.
They are one of our leading partners....Along with other countries, we are prepared to facilitate this process.
It has tie-ups with more than 1,000 companies, although JLR and Tata are its leading partners and conduct their advanced research at the site.
The latest UN statistics show that a lack of funding is leading partners to withdraw and resulted in the closure of 91 of the 250 cholera treatment facilities in Haiti in 2014.
The blunt approach backfired, when leading partners like Georges Ralli, who advises Jean-Marie Messier of Vivendi Universal, and Gerardo Braggiotti, the deal maker behind Pirelli's bid for Olivetti, threatened to leave.
