Muriel Wheldale Onslow (31 March 1880 – 19 May 1932) was a British biochemist, born in Birmingham, England.
She was married to biochemist Victor Alexander Herbert Huia Onslow, second son of the 4th Earl of Onslow.
She studied the inheritance of flower color in the common snapdragon further contributing in the concern of biochemistry pigment molecules in plants such as anthocyanins.
She attended the King Edward VI High School in Birmingham and then matriculated at Newnham College, Cambridge in 1900.
At Cambridge she majored in botany.
She received no degree from Cambridge, despite taking First Class Honors in both parts of the Natural Sciences Tripos, because Cambridge did not award degrees to women until 1948.
Onslow later worked alongside Bateson's genetic group in Cambridge, providing expertise in biochemical genetics and investigating the inheritance of petal color in Antirrhinum (snapdragons).
She was one of the first women appointed as a lecturer at Cambridge, after moving to the Biochemistry department.
A play was written about her and three other female biochemists.