Pittsburgh's first top-10 draft pick in 19 years is officially under contract.
As with all first-round contracts, Bush's deal includes a fifth-year team option.
Bush made his debut with the team on Friday at the start of Pittsburgh's rookie minicamp.
Since 2017, Bush was just one of three FBS players with 150-plus tackles, 10-plus sacks and 10-plus PBUs.
In the Steel City, Bush figures to slide right into the inside linebacker slot that was abruptly vacated two years ago after Ryan Shazier suffered a career-threatening spinal injury. That position was filled last year by Jon Bostic and Vince Williams. But given the draft capital Pittsburgh gave up to acquire him, Bush should be in the starting lineup in Week 1.