The team waived McDowell with a non-football-injury designation prior to their first practice of training camp Thursday. Seattle also placed Kam Chancellor on the reserve/physically unable to perform list, an expected move after the Pro Bowl strong safety and team captain suggested on social media earlier this month that his neck injury would prevent him from playing again.
Chancellor won't count against the Seahawks' 90-man roster while on the PUP list and is officially ineligible to play in 2018.
The Seahawks made McDowell their top draft pick in 2017, choosing him 35th overall out of Michigan State with the hope that he could step in right away and help their pass rush. But he never played a down for Seattle after suffering what the team described as a severe concussion during an ATV accident before training camp last summer.
"It always was disappointing," coach Pete Carroll said of McDowell's situation. "This whole process has been disappointing because he had a real upside. We took a big pick to take him and all that, and unfortunately it didn't happen. We made a move last year because he wasn't here, so that just shows you how important he was."
McDowell spent his rookie season on the non-football-injury list. He was arrested in December on a disorderly conduct charge following a dispute at an Atlanta-area nightclub, later writing in an apology posted to Twitter that he was embarrassed by the incident.
McDowell's release was considered a formality, with no sign that he was any closer to being medically cleared by the Seahawks.
The Seahawks also waived third-year cornerback DeAndre Elliott with a failed-physical designation. Elliott missed last season after dislocating his ankle in Seattle's final preseason game. With the roster spots freed by the moves with McDowell and Elliott, Seattle signed tight ends Kayaune Ross and Je'Ron Hamm.
Both of the Seahawks' projected starting defensive ends are beginning camp on the sideline. Carroll said Frank Clark had a recent wrist operation and Dion Jordan has a new, unspecified injury that's unrelated to his knee surgery from earlier this offseason. Jordan is on the active/physically unable to perform list and, according to Carroll, will be out "a few weeks."
Tight end Ed Dickson, another projected starter, is being held out with what Carroll called a minor groin injury. He is on the active/non-football-injury list.