I rent a property that I partly use as my residence and partly for professional purposes. My partner and I are planning to get married. Will she automatically become a co-holder of the lease with me?

No. The co-tenancy rights granted to spouses under Article 1751 of the French Civil Code apply only to leases for premises used exclusively as a family residence. Since the property is used for both residential and professional purposes (mixed use), your spouse will not automatically become a co-holder of the lease. This position has been confirmed by case law, notably by the French Court of cassation (Civ. 3rd, 28 January 1971).