Privilege belongs to the client and can be waived only by the client through their informed consent. The client's compelled or unintended disclosure does not constitute waiver; only voluntary disclosure to a third party constitutes waiver. However, waiver can occur in the absence of an intention to waive, where fairness and consistency so require. Fairness only applies where the information sought to be disclosed is relevant to the issues in the proceeding.

The common-interest doctrine is an exception to the rule that disclosure of privileged information to a third party waives solicitor-client privilege. The exception applies where privileged information is confidentially shared among parties pursuing a common goal or seeking a common outcome. Legal opinions can be shared without loss or waiver of privilege, where such sharing of information facilitates the completion of a transaction because the parties are able to become informed of the respective legal opinions of others. Parties have been found to have a sufficient common interest where they "shared a united front against a common foe"; they wished to see the successful completion of a commercial transaction; and when a fiduciary duty has been found to exist between them.