Van Es became assistant to the PSP parliamentary party in 1975. During the 1981 election she was elected into parliament. Since 1985 she was chair of the parliamentary party, which after the 1986 election was represented only by her. In the 1989 election the PSP combined forces with the communist Communist Party of the Netherlands and the progressive Christian Political Party Radicals and the Evangelical People's Party under the name GreenLeft. In November 1990 just before the GreenLeft was formed a separate political party Van Es left politics in order to "make room for new GreenLeft faces" and because she had difficulty combining motherhood and her place in parliament. She was a consciously single mother since 1988. She was replaced as an MP by party-member Leoni Sipkes.
After her political career, Van Es worked for the broad casters VPRO and NOS. In 1996 she married MP Maarten van Traa, with whom she had a relationship since 1990. In October 1997 Van Traa died during a car crash. After her journalist work, Van Es led the political-cultural centre De Balie in Amsterdam and chaired the GGZ-Netherlands, a health organization, between 2002 and 2007. In 2001 she was asked by the cabinet to help Máxima Zorreguieta, then the future wife of Willem Alexander integrate in the Dutch society. Between 2002 and 2004 she was a member of the committee-Dijkstal which studied the salaries for politicians and high ranking civil servants. Since november 2007 she is director-general government and Kingdom relations, one of the highest ranking civil servants within the ministry of Home Affairs and Kingdom relations.