Moffitt (6-foot-4, 319 pounds) has 15 starts in two seasons after the Seahawks drafted him in the third round out of Wisconsin in 2011.
He started nine games as a rookie before suffering a knee injury. He started six games last year, four at right guard and two at left, as the Seahawks made the playoffs.
“John’s a tough and versatile lineman who will be in the mix for us upfront,” coach Rob Chudzinski said.
Moffitt was attractive to the Browns because right guards Shawn Lauvao and Jason Pinkston will miss the start of the season with ankle injuries. Lauvao had surgery and Pinkston sustained a high ankle sprain Thursday vs. the Lions.
Rookie seventh-rounder Garrett Gilkey was forced into the starting lineup vs. the Lions, but Moffitt could quickly take over.
“We continue to look each day of the year for any opportunity to improve out roster,” CEO Joe Banner said.
Sanford was expendable because the Browns have an excess of defensive linemen as they switch to the 3-4 scheme. He is better suited for a 4-3.