Welch had prosecuted controversial cases against the late Sen. Ted Stevens, R-Alaska, and two intelligence officials who provided information to journalists.
The court documents reviewed by the Legal Times said the Massachusetts-based Welch planned to go into private practice but did not reveal where.
Politico said Welch's colleagues have described him as a tenacious and talented career prosecutor, though his high-profile prosecutions of Stevens and the two intelligence officials both ran into problems involving failure to turn over discovery evidence to the defense.
Welch was the subject of an internal Justice Department investigation and a separate court-ordered probe for his actions in the Stevens case. Stevens, who died in an August 2010 plane crash in Alaska, was cleared in both inquiries.