Cowell played 81 games for the club at right-back during the Second World War but he did not make his Football League debut until playing against Barnsley on 1st February 1947. He played in 13 games that season. The team that year included Joe Harvey, Len Shackleton, Tommy Walker, Jackie Milburn, Ernie Taylor, Frank Brennan and Charlie Wayman.
In the 1947-48 season Newcastle United won promotion to the First Division. That year he played in 19 league games but the following season he established himself as the club's regular right-back.
Stan Seymour returned as manager in December 1950. Newcastle United finished 4th in the 1950-51 season. Once again Jackie Milburn was top scorer with 17 goals in 31 league games. The club also enjoyed a good FA Cup run beating Bolton Wanderers (3-2), Stoke City (4-2), Bristol Rovers (3-1) and Wolverhampton Wanderers (2-1) to reach the final against Blackpool.
The defences were in control in the first-half. The deadlock was broken in the 50th minute when Jackie Milburn collected a pass from George Robledo to fire home. Five minutes later, Ernie Taylor cleverly back-heeled the ball and Milburn scored with a powerful shot from 25 yards. Cowell had won his first FA Cup winners' medal.
Newcastle United had another good FA Cup run in the 1951-52 season, beating Aston Villa (4-2), Tottenham Hotspur (3-0), Swansea City (1-0), Portsmouth (4-2), Blackburn Rovers (2-1) to reach the final against Arsenal. The London club had finished 3rd in the First Division championship whereas Newcastle managed only 8th place, their lowest position since promotion in 1948.
In the 19th minute Wally Barnes was injured in a tackle with Jackie Milburn. He tried to carry on but he was forced to leave the field in the 35 minute. Arsenal's ten men fought magnificently against the marauding Newcastle forwards. They held out until the 85th minute when George Robledo headed in a Milburn cross. Newcastle had become the first team to retain the FA Cup since Blackburn Rovers in 1891.
According to Jackie Milburn, Cowell "was the best uncapped full-back I've known". Paul Joannou points out in The Black 'n' White Alphabet: "Cowell was a solid defender, brave and tremendously quick to make up lost ground."
Newcastle also had a good FA Cup run in the 1954-55 season, Plymouth Argyle (1-0), Brentford (3-2), Nottingham Forest (2-1), Huddersfield Town (2-0), York City (2-0) to reach the final against Manchester City. Newcastle's star player, Jackie Milburn, later recalled how the game started: "I won a corner on the right and Len White ran over to take it. Manchester City's captain, Roy Paul, was standing next to me as Len placed the ball, but he suddenly yelled, 'Bloody hell, I should be marking Keeble,' so off he darted to find big Vic, who was more widely noted for his prowess in the air. Len fired the ball in my direction and there was I standing all alone like Grey's Monument. I headed the ball past their keeper, Bert Trautmann and that was it."
The situation got worse for City when Jimmy Meadows suffered a serious knee injury in the 18th minute. Just as in 1952 Newcastle had just ten men to beat. Despite this disadvantage City equalized when Bobby Johnstone beat Ronnie Simpson with a diving header after good work from Joe Hayes.
In the second-half Newcastle United made their numerical advantage count. According to Jackie Milburn, the Newcastle captain, Jimmy Scouler, was the best player on the pitch: "Scoular kept spraying great crossfield balls to Bobby Mitchell and between them they tore City apart." Charlie Buchan later commented: "I have never previously seen a wing-half display as good as that of Scoular's in any big game."
In the 53rd minute Bobby Mitchell made a run down the wing before scoring from an acute angle. Soon afterwards George Hannah scored from a pass from Mitchell. Newcastle United had won the FA Cup for the third time in five years and Cowell had won three cup winners' medals.
Cowell was badly injured during a friendly in Germany during a summer tour in 1955. Although only 33 years-old Cowell was forced to retire from the game. He had played 327 games for the club.
Bobby Cowell died in Newcastle upon Tyne on 11th January 1996.