This is a excerpt from USAJobs the entry website for Federal Employment:
“Q: What if I am an ex-offender?
A: Being an ex-offender does not prevent you from obtaining Federal Employment. OPM or the hiring agency considers your criminal conduct in determining your suitability but there are no general prohibitions against hiring you. We consider a number of relevant factors such as the duties of the positions you have applied for, the nature and recency of the misconduct, and any evidence of rehabilitation. Although there are no general prohibitions against employing you in the Federal Government, there are some regulations which will prohibit you from working in certain positions if you have a specific conviction. The most common situation involves being convicted of misdemeanor domestic violence crimes under Federal or State law. These persons are “prohibited form employment in any position requiring the individual: to ship, transport, possess, or receive firearms or ammunition” (Public Law 1-4-208 Omnibus Consolidated Appropriations Act of 1997) Other statutory or regulatory debarments exist, but are rarely applicable. They cover debarment from Federal employment from such offenses as treason, inciting rebellion against the U.S., willful and unlawful destruction of public records, or knowingly and willfully advocating the overthrow of the U.S. Government. It is important for you provide all the required information about your criminal record when you apply for Federal employment. Then, either OPM or the employing agency can determine early if a specific prohibition exists”.
Link to USAJobs: http://www.usajobs.gov/