Written by attorneys · grounded in primary & secondary sources — see below
A professional conduct rule that bars a lawyer who has formerly represented a client in a matter from later representing another person in the same or a substantially related matter when the new client's interests are materially adverse to those of the former client. The prohibition applies unless the former client gives informed consent confirmed in writing. The rule protects the former client's expectation that confidential information will not be used against it in related proceedings.
Sources & Authorities· 4 primary sources
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Model Codes
Course Outlines
How it applies
Common Examples
2
Prospective Client Information Use
Roger Ramirez consulted Patel about suing his former employer for misappropriating code. During the meeting Roger described the employer's confidential repository structure and product timelines. Patel declined the representation. Months later the employer asked Patel to handle a licensing deal involving similar software. Patel considered relying on the details Roger had shared. Because the information came from a prospective client, Rule 1.18(b) extends Rule 1.9 protections and bars its use absent consent.
Imputed Former Client Conflict
Maya previously defended Redstone Produce in a contamination case while at another firm. She later joined BrightFork, which now seeks to sue Redstone on behalf of Harbor Grill in a related food safety class action. Maya is screened from the matter, receives no fee share, and Redstone receives prompt written notice of the procedures. The prohibition arises under Rule 1.9(a) from Maya's prior association, yet the firm may proceed because the required safeguards are in place.
Common questions
Frequently Asked
4
What three elements must be shown to trigger disqualification under Rule 1.9(a)?+
The matters must be the same or substantially related. The new client's interests must be materially adverse to the former client's interests. The former client must not have given informed consent confirmed in writing. Each element is examined separately against the specific facts of the prior and current representations.
Supporting sources
Does the substantial relationship test require that the new claims be identical to the prior matter?+
No. The test is satisfied when the matters share the same transaction or legal dispute or when there is a substantial risk that confidential information from the prior representation would be relevant. Overlap in key contractual provisions or factual issues can establish the connection even if the new claims address later events.
When does information obtained from a prospective client receive the same protection as information from a former client?+
Rule 1.18(b) provides that a lawyer who learns information from a prospective client shall not use or reveal it except as Rule 1.9 would permit with respect to information of a former client. The protection applies even when no client-lawyer relationship is formed.
Supporting sources
How can a firm avoid imputation of a Rule 1.9(a) conflict when a lawyer joins from a prior firm?+
The firm must timely screen the disqualified lawyer from participation, ensure the lawyer receives no part of the fee, and promptly give written notice to the affected former client describing the screening procedures. These steps satisfy the requirements of Rule 1.10(a)(2) and permit the firm to proceed.
Supporting sources
Professional ResponsibilityConflicts of interest · Former client conflictsMPREFoundational