Together with a very young Paulino Alcántara, Francisco Bru and Romà Forns, Greenwell subsequently helped Barcelona win the Catalan championship in 1912–13 and 1915–16.

After retiring as a player, he was appointed manager of Barcelona by the club president, Joan Gamper, and made his managerial debut on 7 July 1917 in a 3–1 win over CE Europa.

He survived early calls for his resignation after experimenting with Alcántara as a defender and went on to lead the club to four Campionats de Catalunya and two Copas del Rey.

[1] As well as Alcántara, the Barça team under Greenwell also included Sagibarba, Ricardo Zamora, Josep Samitier, Félix Sesúmaga and Ferenc Plattkó.

At Barcelona, Greenwell was noted for his innovative approach to tactics, focussing on developing a passing game and building attacks from the back rather than concentrating on dribbling past opponents.

The 1935–36 season would prove to be the last time he managed a Spanish club, finishing in the Segunda División with Sporting de Gijón and missing out on promotion to La Liga.

Colombia, Argentina, Bolivia and Brazil all withdrew before the competition started, so the remaining five countries, Chile, Ecuador, Paraguay, Uruguay and Peru formed a single mini-league with each team playing all the others once.

In 1940, Greenwell moved to the Colombian port city of Barranquilla, and worked with the Colombia national team in their build-up to the 1942 Central American and Caribbean Games.

However, the city's games were postponed due to the worsening political situation during World War II, eventually being held in 1946.