The partner of filmmaker Peter Jackson, Walsh has contributed to all of their films since 1989: as co-writer since Meet the Feebles, and as producer since The Lord of the Rings Trilogy.

Occasionally taking time off to perform in a punk band named The Wallsockets, she attended Victoria University of Wellington majoring in English literature and graduating in 1981.

[2] Walsh got her screen break writing material for New Zealand producer Grahame McLean on 1983 television film A Woman of Good Character (It's Lizzie to those Close).

[2] Walsh met Peter Jackson in the mid-1980s during the final stages of production on his low-budget movie Bad Taste, in which aliens serve humans as fast food.

[3] The couple then reteamed with writer Stephen Sinclair on the horror-comedy film that they had begun writing before Feebles, the zombie movie Braindead (retitled Dead Alive in the United States, 1992).

Walsh, Jackson, and Boyens continued their screenplay work together for the 2005 remake of King Kong, which was given the green light by Universal after the Rings trilogy's success.