At some point during the interview process, most law firms or companies will ask a candidate to complete an application or provide responses to a lateral attorney questionnaire. Often times, this entails disclosing reasons for leaving a prior employer and any past criminal conduct. Between the two requested disclosures, it is not uncommon to have something in your past that could potentially be an issue.
Not all situations are the same so the manner in which you deal with such disclosures may vary. That said, it is always important to be forthcoming with such information. Employers almost always find out at some point and you would hate to be terminated for simply failing to disclose this information. How much attention you give to disclosing these past challenges can be the tricky part. If something is relatively minor, perhaps just disclosing it on the requisite form is sufficient. However, if you think the incident may affect the hiring decision, it might be best to address the issue in person as well. Not only do you get a chance to explain the incident and related extenuating circumstances, but it also gives you a chance to convey remorse or at least offer a human element to the situation (as opposed to someone just reading about it).
Everyone makes mistakes and sometimes they can catch up with us during the hiring process. While there are some incidents in which an employer has no choice but to stop the process, most will offer an opportunity for you to explain the situation and demonstrate why it should no longer be an issue.