Mariella Norma Borthwick (25 July 1862 – 13 June 1934) was a British artist and writer and an Irish language activist.

From an early age she displayed an interest in the culture of Ireland, and learned the Irish language at the Southwark Literary Society in London.

In January 1895, Borthwick joined the Gaelic League in London, and while living on Markham Square, Chelsea acted as its treasurer.

[4] Borthwick assisted Eoin MacNeill in the publication of An Claidheamh Soluis, going on to write a series in Irish for St Patrick's magazine from 1900 to 1903, under the name "Fear na Móna".

The company also published Father Peadar Ua Laoghaire's Mo Sgéal Féin, with Borthwick preparing a dictionary for the book.

By this point Borthwick was paralysed and unable to speak, having contracted encephalitis lethargica or sleeping sickness in the wake of World War I.