Born in 1959, Twombly studied at the Rhode Island School of Design, where she became interested in type design and typography under Professor Charles Bigelow. After graduation, she embarked on a Master's course in digital typography at Stanford University also under Bigelow. She went on to work with him at the Bigelow & Holmes studio.
She won first prize in the Morisawa Typeface Design Competition in 1984 for her typeface Mirarae, a Latin design which went on to be licensed and released by Bitstream.
Since 1988 she has been a staff designer at Adobe Systems, and was awarded the prestigious Prix Charles Peignot at the 1994 ATypI conference in San Francisco, given to outstanding type designers under the age of 35.
Twombly retired from type design in 1999.