She graduated from Vilnius Pedagogical University in 1986 and worked as a teacher until 1998. She started lecturing at the Mykolas Romeris University in 2000.
Vainiutė was minister of justice in 2016-2018. Afterwards, in 2018-2021, she was a parliamentary ombudswoman.
In 2003-2009, Vainiutė served as adviser on legal affairs to then President Valdas Adamkus. Later, she was the senior legal consultant at the Office of the President in the first term of office of then President Dalia Grybauskaitė.