Blagojevich last week became the first Illinois governor ever to be impeached.
Ellis oversaw the legal work of the state House committee that recommended the move against the Democratic governor. The report Ellis helped prepare led the full House to vote 114-1 in favor of impeachment.
The Senate trial begins later this month.
As House counsel, Ellis is a top aide to House Speaker Michael Madigan, a Chicago Democrat and vocal Blagojevich critic.