Nixon Peabody has officially agreed to acquire Chicago’s Ungaretti & Harris, taking on about 100 lawyers in the Windy City, making it the Boston-based Am Law 100 firm’s second-largest office.

The Am Law Daily reported last week on the merger discussions between Nixon Peabody and Ungaretti & Harris, which were first reported by Crain’s Chicago Business. The tie-up, officially announced Monday, will be effective as of Feb. 1 and operate under the Nixon Peabody banner.