When Carey began his international career in 1937 there were, in effect, two Ireland teams, chosen by two rival associations. Both associations, the Northern Ireland-based IFA and the Republic of Ireland-based FAI claimed jurisdiction over the whole of Ireland and selected players from the whole island. As a result several notable Irish players from this era, including Carey played for both teams. In September 1946 Carey, along with Bill Gorman, even played for both teams within three days of each other, both times against England. On 28 September at Windsor Park he played for the IFA XI in a 7–2 defeat. Then on 30 September at Dalymount Park he played for the FAI XI in a 1–0 defeat.
Between 1937 and 1953 Carey made 29 appearances and scored 3 goals for the FAI XI, making his debut against Norway on 7 November 1937 in a team that also included Jimmy Dunne and fellow debutant, Kevin O'Flanagan. The game which was a qualifier for the 1938 FIFA World Cup finished as a 3–3 draw. He scored his first goal for the FAI XI in a 3–2 win against Poland on 13 November 1938 and scored his second in the very next game, a 2–2 draw with Hungary on 19 March 1939. Carey captained the FAI XI on 19 occasions. On 21 September 1949, he was captain when an FAI XI defeated England2–0 at Goodison Park, becoming the first non-UK team to beat England at home. Carey scored his third goal, a penalty, for the FAI XI in a 2–2 draw with Norway on 26 November 1950. He played his last game for the FAI XI on 25 March 1953 in a 4–0 win over Austria.
One of Carey's earliest experiences as a coach came when he was still an active player; he took charge of the Ireland team at the 1948 Olympics. Ireland lost 3-1 to the Netherlands in the opening round in a game played at Fratton Park. Carey retired as a player in 1953 and almost immediately accepted the position as manager of Blackburn Rovers. In 1958 he guided Rovers into First Division. He then became manager at Everton but, despite leading them to fifth place in the 1960–61 season, their highest post-war position, he was infamously sacked in the back of a taxi by director John Moores. As a result the infamous fans jibe, 'Taxi for xxxxxx!' has become a staple insult offered to any manager facing the threat of the sack. He next managed Leyton Orient and took them into the First Division in 1962, their only season in the top division. However his greatest success as a manager came with Nottingham Forest. In 1967 he guided them to the FA Cup semi-finals and to second place in the First Division behind his former club Manchester United. Between 1955 and 1967 Carey also served as team manager of the Republic of Ireland. However Carey had very little power as the team itself was chosen by a selection committee.