Model Rule 1.9: Duties to Former Clients
Rule 1.9 limits what a lawyer can do against or for people connected to a client the lawyer used to represent. It bars taking on a new matter that is the same or substantially related to the old representation if the new client's interests are materially adverse to the former client, unless the former client gives informed consent confirmed in writing. It also bars using or revealing the former client's confidential information to that former client's disadvantage, except as the rules on confidentiality would otherwise permit.
When it applies
This comes up whenever a lawyer switches sides, changes firms, or is approached to sue someone the lawyer (or the lawyer's old firm) previously represented; the MPRE tests whether facts create a "substantially related" matter and material adversity, and whether consent was properly obtained. It frequently overlaps with imputation questions under Rule 1.10 when a lawyer moves firms.
What the rule requires
- A lawyer may not represent a new client in the same or a substantially related matter if that new client's interests are materially adverse to a former client's interests.
- For a lawyer who personally represented the former client, this bar applies whether or not the lawyer can show that confidential information was actually acquired. The substantial-relationship test itself addresses that risk.
- A lawyer who leaves a firm may not knowingly represent a person in the same or a substantially related matter in which the lawyer's former firm represented a client whose interests are materially adverse to that person, if the lawyer personally acquired protected information about that client that is material to the matter, unless the former client gives informed consent confirmed in writing.
- The lawyer must not use information relating to the former representation to the former client's disadvantage, except when the information has become generally known or the rules otherwise allow disclosure.
- The lawyer must not reveal the former client's confidential information except as the confidentiality rule would permit for a current client.
- Conflicts under this rule can be waived only through informed consent, confirmed in writing, from the affected former client.
Exceptions
- No violation if the former client gives informed consent, confirmed in writing, to the new adverse representation.
- The ban on using former-client information to the former client's disadvantage does not apply once the information has become generally known. This exception does not permit revealing the information. It also does not cure a same or substantially related matter conflict.
- No violation if the new matter is not the same or substantially related to the former representation, even if adverse.
- A lawyer who did not personally acquire relevant confidential information while at a former firm is not automatically barred, even though other lawyers at that firm were involved.
How the MPRE tests Model Rule 1.9
- Students forget that Rule 1.9 requires materially adverse interests AND a substantial relationship between matters—adversity alone or similarity alone is not enough.
- Confusing Rule 1.9 (former client) with Rule 1.7 (current client conflicts)—the key trigger is whether the attorney-client relationship in the old matter has actually ended.
- Overlooking that consent must be informed consent confirmed in writing, not just verbal permission.
- Missing the imputation angle: an individual lawyer's disqualification under 1.9 can spread to the whole firm under Rule 1.10 unless screening or consent applies.
Example
Lawyer represented a small manufacturer in a contract dispute with a supplier and learned confidential pricing strategy during that work. Two years later, after the manufacturer relationship ended, the lawyer is asked to represent the same supplier in a new breach-of-contract suit against that same manufacturer arising from a similar pricing dispute. Because the new matter is substantially related to the old one and the supplier's interests are materially adverse to the former client's, the lawyer may not take the case without the former client's informed consent confirmed in writing.
Related rules
- Model Rule 1.7: Conflict of Interest: Current Clients
- Model Rule 1.10: Imputation of Conflicts of Interest: General Rule
- Model Rule 1.11: Special Conflicts of Interest for Former and Current Government Officers and Employees
- Model Rule 1.12: Former Judge, Arbitrator, Mediator or Other Third-Party Neutral
- Model Rule 1.18: Duties to Prospective Client
- Model Rule 1.6: Confidentiality of Information
On the MPRE
A plain-English summary of the ABA Model Rule, not the rule text. Your jurisdiction's version of the rule controls in practice.