Short answer. It turns it into an agency. Article 2149 provides that the owner's ratification of the management produces the effects of an express agency — as though you had been authorised from the start — and this holds even if the venture was not successful. Ratification looks back to the beginning, not merely forward.
What the law says
The ratification of the management by the owner of the business produces the effects of an express agency, even if the business may not have been successful.
Civil Code, Article 2149 — Ratification of the Management. Read the full provision →
From uninvited management to agency
While you manage another's affairs without authority, your position is governed by the rules on officious management, which are cautious about a role no one asked you to take. Article 2149 changes that the moment the owner approves what you did: the ratification of the management by the owner of the business produces the effects of an express agency. Approval converts the relationship. You are treated as if the owner had appointed you his agent, and the more settled body of agency law governs what you did in his name, in place of the officious-management regime.
What the effects of an express agency change
Being treated as an agent, rather than an officious manager, has real consequences. An agent acting within his authority binds the principal to the acts done in his name, and can look to the principal for what agency entitles an agent to — the standard of care, reimbursement and the allocation of risk shift onto that footing. Because ratification carries the effects of an express agency, it reaches back and validates the management as authorised, so acts that were done for the owner but without his prior mandate are placed on the same footing as if he had commissioned them.
Success is not the test
The article is careful to add that ratification produces these effects even if the business may not have been successful. Approval is not a reward reserved for a management that turned a profit. An owner may ratify a management that failed — because the manager acted properly, or because the owner accepts what was done in his name regardless of outcome — and the ratification still carries full effect. The consequences flow from the owner's approval of the management, not from whether the venture ultimately prospered, so a poor result does not by itself deprive ratification of its force.
Why ratification is worth seeking
For a manager who acted in good faith, the owner's approval is the cleanest outcome available. It resolves the awkward questions that hang over uninvited management — whether expenses are recoverable, who bears the risk of what went wrong — by recasting the whole episode as an authorised agency. For the owner, ratifying is a deliberate choice with binding effect, not a mere courtesy, since it adopts the manager's acts as his own. Anyone in this position should understand that once given, ratification is what fixes the legal character of everything the manager did in the owner's name.