[6] Mitchell's brother Edward passed out of Sandhurst in 1916[7] and died near the end of the First World War, while serving as a Second Lieutenant in the Royal Air Force.

[12] In the 1930s, Mitchell was corresponding with Hanna Sheehy-Skeffington about arrangements for meetings of the Women Writers’ Club and the Roger Casement Committee, and about other matters,[13] such as infiltration of the political system in the Irish Free State by fascist and reactionary ideas.

[14] The two met many times, and in 1946 Mitchell wrote an obituary of Sheehy-Skeffington for the Connolly Association’s Irish Democrat, concluding that "... her loss to the London-Irish is as great as that to those at home.

"[15] In 1935, Mitchell’s book Traveller in Time, set in Ireland in 1942, explores a fantastic development of the age of television in the context of Irish history.

[16] Colm MacColgan, her traveller, uses his invention of "Tempevision" to tune in to events at different times and places in the past, observing the impacts of the Irish around Europe and beyond.

[17] A glowing review of the work in An Gaedheal reported that Mitchell was one of the most enthusiastic members of the Gaelic League in London and urged its readers "GAELS, read this book!

[18] While he was writing Homage to Catalonia,[11] George Orwell reviewed Mitchell's Storm over Spain (1937) for Time and Tide and commended its well-informed analysis, adding that it was "written by a Catholic, but very sympathetic to the Spanish Anarchists".

[11] Fredric Warburg, the publisher of Storm Over Spain, later wrote that the book had been "a flop", but added that it was "the only pacifist study I ever read of the Spanish War".

[20] In 1939, Mitchell was highly critical of the Irish leftists for their views on the Molotov–Ribbentrop Pact and wrote to Desmond Ryan in September "Brian O'Neill, Bloomsbury, and Daiken will sing Russia right or wrong.

[30] In November 1953, The London Gazette recorded Miss Marian Houghton Mitchell as the personal representative of James Garrett Peacocke, deceased, retired merchant seaman, of Walworth, who had died in September of that year.

[32] She relied largely on work by Arteche for her two biographies of Basques on Pacific voyages of discovery, Juan Sebastián Elcano and Andrés de Urdaneta.

[33] Of her Elcano the First Circumnavigator (1958) the British Book News said that while written for the general reader, it was the result of wide reading and research in Spanish archives.