From the Victorian country town Cobden, Merrett was a small footballer who was a keen Richmond fan who wanted to play league football for the Tigers. At 16 years of age, Merrett was rejected by Richmond legend Jack Dyer because of his light frame, but he was given another opportunity at Victoria Park, where he stood out in a set of practice games for Collingwood just before the 1950 season. It was initially thought by followers and players that he would be 'killed' because of his size. He made his debut for Collingwood in 1950. At the age of 16 he was one of the youngest players in the VFL. Merrett played as a wingman and won respect for the accuracy and speed of his stab kick. He became one of the best players in the competition despite his unusually small stature for a league footballer. In 1952, Merrett came equal sixth in the Brownlow Medal, and won a top three finish in the Copeland Trophy. A year later he again finished in the top 10 in the Brownlow Medal and celebrated the 1953 premiership with the Magpies, when he was one of the best players in the Grand Final. In years that followed, Merrett performed consistently and he continued to be regarded as one of the best kicks in the league, as well as one of the best wingmen. He played in two losing Grand Finals in 1955 and 1956. In 1958, Merrett changed roles to become a rover, and it succeeded. He won the club Best and Fairest and the Pies also won the 1958 flag, with Merrett named best on ground. In 1959, he again starred as a rover, winning a second consecutive Copeland Trophy, and finishing in the top 10 in the Brownlow Medal for a third time.
Retirement
A second broken leg in 1960 saw Merrett miss most of the season and, due to doubts about the strength of his leg, aged 26, he retired, feeling his best football was past. He played 180 games in 11 seasons and kicked 148 goals. He was also a dual Best and Fairest and premiership player, and Victorian representative on seven occasions. He was a regular panelist on the ABC's Football Round-up, which he and other panelists discussed the Saturday round of VFL football. In 1997 he was included in the Collingwood Football ClubHall of Fame and Team of the Century, on the wing.
