She said she will be leaving to pursue 'other projects', although she declined to comment on the work's nature.
Hooper will continue to act as a consultant for Nexus on an ad hoc basis.
Nexus group CEO Jim Horsley said he will take over as acting consumer MD - heading a team of 45 - while recruitment takes place for Hooper's replacement.
Her departure follows that of up to four directors and associate directors who have quit in the past 12 months.
Horsley said: 'What we have been doing over the past 18 months is building the business and changing it. When you are changing a business, some people decide their future is better elsewhere.'
Hooper was formerly managing director of consumer firm Kable PR, which closed last November following financial difficulties (PRWeek, 23 November 2001).