UnitedHealth Group will promote one of its top insurance executives to replace Brian Thompson, the slain CEO of its UnitedHealthcare arm.

The new CEO of Minnesota-based UnitedHealthcare takes the helm of a company whose former leader was killed in December.

UnitedHealthcare announced a new CEO on Thursday, filling in the spot after Brian Thompson was shot and killed in December in what authorities have called a targeted attack.

UnitedHealth Group Inc. promoted the head of its Medicare health plan business to lead the company’s broader insurance division, filling the job previously held by slain executive Brian Thompson. Tim ...