Following her graduation, she worked as financial policy officer at the Dutch Ministry of Transport and as a civil servant for the municipality of Amsterdam.

She obtained her PhD in 2000 from the faculty of law of the VU University of Amsterdam with a doctoral dissertation on privatization of government services.

In September 2009 Sylvester was appointed as acting mayor of the Naarden, serving until its amalgamation to the new municipality Gooise Meren in January 2016.

[3] Sylvester became deputy National Ombudsman the following month, and she appeared on de Volkskrant's list of most influential Dutch people in late 2019.

Sylvester cited several comments by members of the Schoof cabinet to argue that it was increasing the risk of government discrimination.