The phrase "lead partner" refers to a person or organization that takes the main responsibility in a partnership or collaboration. They are in charge and play a primary role in leading the group or project. Full definition
For instance, if you are just leading your partner on, it is right to cut him or her loose. (relationshipsdatingtips.com)
Having begun his career as a journalist, he then became lead partner at a branding and marketing agency. (shiftcentral.com)
Take advantage of savings and special offers from over 30 carefully selected industry - leading partners from the REALTOR Benefits ® Program, their official member benefits resource. (rismedia.com)