While living and playing cricket in Nelson before the war, Constantine had made plans for a future legal career.
James helped him with his studies for a short time, and he later worked in a local solicitors' office.
In 1944 he enrolled as a student in the Middle Temple, London.
To finance his studies, he continued his professional cricket career in Bradford until 1948, and supplemented his income by coaching: at Trinity College, Dublin, in 1947 and in Ceylon in 1953.
Constantine also extended his work in journalism and broadcasting, as a cricket reporter and as a radio commentator when the West Indies toured England in 1950.
He also wrote several cricket books, probably with the help of a ghostwriter.
Cricket in the Sun (1947) covered his career but also discussed the racism he had encountered and suggested then-radical ideas for the future of cricket, such as a one-day "world cup".
Cricketers' Carnival (1948), Cricket Crackers, Cricketers' Cricket (both 1949) and How To Play Cricket (1951) were more traditional cricket books, which included coaching tips and opinions.

In 1947 Constantine became chairman of the League of Coloured Peoples, a position he held until the League was discontinued in 1951.
In 1948 he was elected president of the Caribbean Congress of Labour, and between 1947 and 1950 was a member of the Colonial Office's Colonial Social Welfare Advisory Committee.
Also in 1950, he became involved in a controversy over the interracial marriage of Seretse Khama, the future president of Botswana.
Constantine lobbied the government on Khama's behalf, organised meetings and even approached the United Nations.
Little was achieved, and Constantine disapproved of the approach of the Labour government and its Prime Minister, Clement Attlee, but declined an opportunity to become a Liberal parliamentary candidate.

Constantine neither enjoyed his legal studies, nor found the work easy, but was determined to prove he could succeed.
His wife kept him motivated, restricted visitors to avoid distractions and forced him to study, making him continue when he was several times tempted to give up.
The family moved to London in 1949; between 1950 and 1954, Constantine passed the required series of examinations, and in 1954 he was called to the bar by the Middle Temple.

Having turned down an offer in 1947 to return to his old employer, Trinidad Leaseholds, in 1954 Constantine agreed to join the same company as an assistant legal advisor.
Uncertain about going back to Trinidad after living for 25 years in England, he nevertheless believed it was a good time to return, particularly as his daughter was moving there to marry.
Before leaving England, he published his book Colour Bar (1954), which addressed race relations in Britain and the racism he had experienced.
It also discussed worldwide racial oppression and how the lives of black people could be improved.
At the time, according to Peter Mason, this was "an explosive, challenging, hard hitting tome, the more so because it came not from a known black militant but from someone who seemed so charming, so unruffled, so suited to British society".
Although not viewed as radical by black audiences, it was aimed at white British readers.
The British press gave it mixed reviews and criticised him for unfairness in parts of the book; other critics accused him of communist sympathies.
While living and playing cricket in Nelson before the war, Constantine had made plans for a future legal career. James helped him with his studies for a short time, and he later worked in a local solicitors' office. In 1944 he enrolled as a student in the Middle Temple, London. To finance his studies, he continued his professional cricket career in Bradford until 1948, and supplemented his income by coaching: at Trinity College, Dublin, in 1947 and in Ceylon in 1953. Constantine also extended his work in journalism and broadcasting, as a cricket reporter and as a radio commentator when the West Indies toured England in 1950. He also wrote several cricket books, probably with the help of a ghostwriter. Cricket in the Sun (1947) covered his career but also discussed the racism he had encountered and suggested then-radical ideas for the future of cricket, such as a one-day "world cup". Cricketers' Carnival (1948), Cricket Crackers, Cricketers' Cricket (both 1949) and How To Play Cricket (1951) were more traditional cricket books, which included coaching tips and opinions.
In 1947 Constantine became chairman of the League of Coloured Peoples, a position he held until the League was discontinued in 1951. In 1948 he was elected president of the Caribbean Congress of Labour, and between 1947 and 1950 was a member of the Colonial Office's Colonial Social Welfare Advisory Committee. Also in 1950, he became involved in a controversy over the interracial marriage of Seretse Khama, the future president of Botswana. Constantine lobbied the government on Khama's behalf, organised meetings and even approached the United Nations. Little was achieved, and Constantine disapproved of the approach of the Labour government and its Prime Minister, Clement Attlee, but declined an opportunity to become a Liberal parliamentary candidate.
Constantine neither enjoyed his legal studies, nor found the work easy, but was determined to prove he could succeed. His wife kept him motivated, restricted visitors to avoid distractions and forced him to study, making him continue when he was several times tempted to give up. The family moved to London in 1949; between 1950 and 1954, Constantine passed the required series of examinations, and in 1954 he was called to the bar by the Middle Temple.
Having turned down an offer in 1947 to return to his old employer, Trinidad Leaseholds, in 1954 Constantine agreed to join the same company as an assistant legal advisor. Uncertain about going back to Trinidad after living for 25 years in England, he nevertheless believed it was a good time to return, particularly as his daughter was moving there to marry. Before leaving England, he published his book Colour Bar (1954), which addressed race relations in Britain and the racism he had experienced. It also discussed worldwide racial oppression and how the lives of black people could be improved. At the time, according to Peter Mason, this was "an explosive, challenging, hard hitting tome, the more so because it came not from a known black militant but from someone who seemed so charming, so unruffled, so suited to British society". Although not viewed as radical by black audiences, it was aimed at white British readers. The British press gave it mixed reviews and criticised him for unfairness in parts of the book; other critics accused him of communist sympathies.
Learie Constantine