Selected 30th overall in April out of Wisconsin, the 22-year-old outside linebacker becomes the third member of his family in the NFL. He joins older brothers J.J. (Houston Texans) and Derek (Los Angeles Chargers).
T.J. Watt was the last of the Steelers' eight draft picks to sign.
"I am a lunch pail kind of guy who yeah, I just got picked in the first round, but I am here to prove that I am worth that pick and I am worth much more than that as well," Watt said earlier this week. "I think some things come easy for me, like the transition over to defense. It came naturally to me, but at the same time there was so much work behind the scenes that no one ever saw. That's what it's so hard to put it into words. It is a lot of God-given ability, but it is so much work that no one will ever see.
"No one will ever know. It's an insurmountable amount of work. That is how you get to places like this and get the opportunity to play for the Pittsburgh Steelers. It all pays off. It really does."
Watt finished the 2016 season at Wisconsin with 17 tackles for a loss and 11.5 sacks, his first as a starter and only his second playing defense after switching from tight end.
"T.J. is a rock solid young man who has a lot of upside," Steelers coach Mike Tomlin said recently. "He doesn't have a lot of experience at the position, but at the same time we saw some things that were exciting to us. His hand usage in particular for a guy with his short resume at the position was exciting. His production speaks for itself. He's just a quality guy and a quality pick for us. We're excited about continuing his development not only as a football player, but as an outside linebacker. That's probably the most exciting element of the T.J. discussion. We are excited about the potential upside and growth given the short length of time he's played the position."