He was selected in the 12th round of the 1942 NFL draft by the Chicago Bears, but delayed a professional career to work for his family's steel business and serve in the U.S. Navy during World War II.

After the war, Daniell played for the Bears in part of the 1945 season before joining the AAFC's Cleveland Browns the following year, serving as the team's first captain.

[3] He played on Ohio State teams that won the Big Ten Conference championship in 1939 and had a 6–1–1 record in 1941.

[4] As a senior in 1941, Daniell blocked a punt in a game against Purdue University that resulted in a safety and made the difference in a 16–14 victory.

[6] Daniell was selected by the Chicago Bears in the 1942 NFL draft, but he delayed his professional career to go back to Pittsburgh and work at the Alloy Manufacturing Company, which his father founded in the 1930s and he and his brother operated.

In one battle he and his men shot down 23 planes in an hour and 20 minutes, which was thought to be a record for a single engagement.

[9] Daniell's salary was $9,000 a year ($140,621 in 2023 dollars), plus $1,000 for serving as the Browns' first captain as the team finished the 1946 season with a 12–2 record and earned a spot in the AAFC championship.

[8] Before the AAFC championship game in December, Daniell was arrested along with teammates Lou Rymkus and Mac Speedie following an altercation with Cleveland police.

[10] Paul Brown fired Daniell after the incident, saying he had "a special obligation to be exemplary in his behavior" because he was the team captain.