She was born of the Big Water Clan, born for the Red House Clan. Tsosie attended Ganado Public Schools. She was a Christian and volunteered with Save the Children Program in Window Rock, Arizona.

She retired from Arizona State University. She loved to weave, sew, do ceramics, and crochet.

Survivors include her two sons; her two daughters; a brother; three sisters; six grandchildren; and two great-grandchildren.

Mary Kate Tsosie was preceded in death by husband Lorenzo Tsosie, and parents Kee and Eleanor John.

Graveside services were held on Feb. 16, 2022, at the Klagetoh Community Cemetery.