Through her mother, Sailigi Tusitala, Marsh is of Samoan and Tuvaluan ancestry and through her father James Crosbie she is of English, Scottish and French descent.

She gained her doctorate from the University of Auckland in 2004 after completing her thesis titled "Ancient banyans, flying foxes and white ginger": five Pacific women writers.

[8] In 2016, Marsh composed and performed the poem "Unity" for Queen Elizabeth II at Westminster Abbey on Commonwealth Day Observance.

[10] In the 2019 New Year Honours, Marsh was appointed an Officer of the New Zealand Order of Merit, for services to poetry, literature and the Pacific community.

[15] Poetry by Marsh was included in UPU, a curation of Pacific Island writers’ work which was first presented at the Silo Theatre as part of the Auckland Arts Festival in March 2020.