Can an attorney represent a client against a previous client, without notification to the previous client? If No, will case be thrown out upon being made known to the Court or must case be appealed on that fact alone? What types of damages are those?

  • 1
    They probably have a conflict of interest, if the attorney knows privileged information about the previous client that's relevant to the case.
    – Barmar
    Apr 11 at 21:43

3 Answers 3


If you look at the American Bar Association model code of ethics, you'd be looking at Rule 1.9 Duties to Former Clients. Every US state will have slightly different verbiage in their code but they'll all agree on the basics.

(a) A lawyer who has formerly represented a client in a matter shall not thereafter represent another person in the same or a substantially related matter in which that person's interests are materially adverse to the interests of the former client unless the former client gives informed consent, confirmed in writing.

So it depends whether this is a "substantially related matter". If Larry the Lawyer prepared Alice's will, for example, that would not prevent him from representing Bob if he wanted to sue Alice for unpaid rent. The will and the rent dispute would not generally be substantially related matters.

Normally, however, lawyers specialize in particular areas of the law so it would be unlikely that a lawyer would be able to represent a client and then sue that same client.

  • employment lawyers however might be tricky: imagine Vinnie the Lawyer is hired to draft the employment contracts that Alice uses to hire people as a Widgeteer. Bob is hired as a Widgeteer and later wants to retain Vinie to litigate against Alice on that particular contract.
    – Trish
    Apr 13 at 20:40

Can an attorney represent a client against a previous client, without notification to the previous client?

The answer from Justin Cave adequately addresses this point.

If No, will case be thrown out upon being made known to the Court or must case be appealed on that fact alone? What types of damages are those?

None of the above. If this happens, the former client may ask the Court to disqualify the conflicted attorney from representing his current client in the case. If the former client doesn't do this, any consequences in the case are waived. It is not a basis for an appeal if no motion for disqualification is filed, it is not a basis for throwing out the case, and it is not the basis for a claim for money damages.

The attorney could also be disciplined by state attorney ethics officials, if someone files a complaint with them. The punishment could range from a private reprimand to disbarment, depending upon the severity of the violation and the attorney's history of previous ethics violations.


It depends

In the rule is slightly different between barristers and solicitors.


A barrister must refuse to accept or retain a brief or instructions to appear before a court if:

(a) the barrister has information which is confidential to any other person in the case other than the prospective client, and:

(i) the information may, as a real possibility, be material to the prospective client’s case, and

(ii) the person entitled to the confidentiality has not consented to the barrister using the information as the barrister thinks fit in the case,

Note that, in general, a barrister must accept a brief referred to them by a solicitor - they cannot pick and choose their clients. A barrister in civil practice is quite likely to come up against former clients, and many criminal defence barristers were former prosecutors and therefore had the Crown as a client.

So having simply had the person as a former client is not sufficient. Neither is knowing confidential information if it is immaterial to the matter at hand.

If they do know material confidential information, they can still act if the person gives permission.


10.1 A solicitor and law practice must avoid conflicts between the duties owed to current and former clients.

10.2 A solicitor or law practice who or which is in possession of information which is confidential to a former client where that information might reasonably be concluded to be material to the matter of another client and detrimental to the interests of the former client if disclosed, must not act for the current client in that matter UNLESS—

10.2.1 the former client has given informed consent to the disclosure and use of that information, or

10.2.2 an effective information barrier has been established.

The first limb of this rule is that the solicitor must avoid conflicts of interest: note that these must be actual conflicts, not apprehended ones. Merely having represented the other party in the past does not, of itself, create a conflict.

The second limb is if they hold confidential information. If they do, they can act if they have permission or they effectively firewall the confidential information. The latter would generally only be feasible in a relatively large firm.

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