Martin was selected Saturday by the Tennessee Titans with the 20th pick in the sixth round (190th overall).
"Markelle is going to be a really good NFL player," OSU head coach Mike Gundy said in a news release. "He's very intelligent and has been a good hitter for us. He can play two positions in the NFL because he's smart. He was a really good leader for us and you never have to worry about him getting into anything off the field. He should be a real good safety in the NFL."
In addition, seven other Cowboys who played major roles in OSU winning the Big 12 Conference championship this past season signed free agent contracts.
Josh Cooper, who finished his career as one of the top 10 receivers in school history, will be reunited with Weeden with the Cleveland Browns. Cooper signed a free agent deal with the Browns almost immediately after the draft ended Saturday afternoon.
Jamie Blatnick, who earned first team All-Big 12 honors this past season, signed as a free agent with the Denver Broncos.
All-Big 12 offensive tackle Levy Adcock and All-Big 12 center Grant Garnet signed free agent contracts with the Dallas Cowboys and Washington Redskins, respectively.
In addition, defensive end Richetti Jones signed with the Arizona Cardinals and wide receiver Hubert Anyiam is heading to San Diego with the Chargers.
Former free safety Johnny Thomas, who did not play in 2011, signed a free agent deal with the New Orleans Saints.