On December 19, 2015, it was announced that Oklahoma's Blake Bell, Adam Shead, and Aaron Ripkowski had all accepted their invitations to play in the 2015 East–West Shrine Game. He raised his draft stock after being impressive during Shrine Game practices. On January 17, 2015, Bell played in the East–West Shrine Game and was a part of Jim Zorn's West team that was routed by the East 19-3.
On March 11, 2015, Bell opted to participate at Oklahoma's pro day, but stood on his combine number and only performed positional drills for scouts and team representatives from all 32 NFL teams. Due to limited experience and a thin draft class at tight end, multiple NFL draft experts and analysts projected Bell to be a fifth round draft pick. He was ranked the ninth best tight end prospect in the draft by NFLDraftScout.com.
Bell was selected by the San Francisco 49ers in the fourth round (117th overall) of the 2015 NFL Draft. He was the fifth tight end chosen in 2015. On May 11, 2015, the 49ers signed him to a four-year, $2.78 million contract that includes a signing bonus of $505,132.
On October 11, 2015, he earned his first career start after Vernon Davis was inactive due to a knee injury. Bell finished the 30-27 loss at the New York Giants with one reception for six-yards. He was a healthy scratch in Weeks 7-8. On November 29, 2015, Bell caught three passes for a season-high 67-yards during a 19-13 loss to the Arizona Cardinals. He saw increased snaps in the Cardinals game after Garrett Celek left the game due to an ankle injury.