Anderson is an important playwright, philosopher and performer, who has been widely written about for his work in general. There is an expansive biography available of his career at Wikipedia. In the UK he was the subject of a great deal of interest, and was frequently described as a ‘playwright, lecturer, and metaphysician’ in the British press. While he didn’t directly produce or write musicals, he was a part of the wider theatre scene and the Black community. He maintained a transatlantic presence throughout the 1930s, perhaps unsurprisingly given his marriage to Doris Sequeira, a white British woman.
He saw his plays produced in the West End, and worked as a lecturer and public speaker, often in churches. Mrs Bourchier produced his play Appearances at the Royalty Theatre, London, in March 1930 with Doe Green, a Black actor, in the lead. In 1932 it was reported that he wanted to revive it so that 200 unemployed men could see it and be addressed by him in the interval, and hear his message of hope. This came to fruition and his play was revived at the Fortune Theatre, he donated his royalties to a charity for the unemployed.
In 1934 he opened a teetotal bar at Shaftesbury Avenue, referred to as a milk bar, though it is unclear how long it lasted for.
He gave lectures across the UK, from Eton School, Edinburgh Rotarians, the Practical Psychology Club of Reading, to Eastbourne Pier and churches in Preston, Lancashire. He spoke about his ideas of “uncommon sense”, that allowed him to pursue the impossible or face unimaginable difficulties, and as a way to circumvent the many problems he had faced. He later published this idea as a book with the same title.
British Newspaper Archive, in particular The Era.
Abramson, Doris E. Negro Playwrights in the American Theatre, 1925-1959. New York : Columbia University Press, 1991. https://archive.org/details/negroplaywrights00abra
Prentiss, Craig R. ““The Full Realization of This Desire” Garland Anderson, Race, and the Limits of New Thought in the Age of Jim Crow.” Nova Religio: The Journal of Alternative and Emergent Religions 17, no. 3 (2013): 84-108. https://doi.org/10.1525/nr.2014.17.3.84