Sullivan, 38, made headlines last June by calling on incumbent Andrea Harrington to resign over her controversial and unsuccessful effort to remove a district court judge from the bench.
The attorney is making criticism of the first-term Democrat and her office the centerpiece of his campaign to date.
“I just don't see some clear leadership there," he told WAMC. "I think that's been shown by a lot of turnover that they've had among their staff, among the attorneys that have worked there.”
At 11 a.m. Monday, he’ll officially announce his run for DA as an independent candidate in downtown Pittsfield’s Park Square. Also declared so far is local trial attorney Timothy Shugrue.