Castell will lead the company's qualitative hothouse, which Ipsos claims combines the flexibility of a specialist boutique with the largest qualitative resource in the UK.
Mike Everett, managing director at Ipsos Mori, said: "We have a truly outstanding team of qualitative researchers. I am absolutely delighted that Sarah will be leading this area and I am expecting substantial growth and innovation in the future."
Castell has been with Ipsos Mori for three years and was with Flamingo International for seven years before that.
The previous head of qualitative research, Andrew Johnson, is still a director with the company and is now heading up the internal communications taskforce.
Talking about her new team, Castell said: "Our team is skilful enough to deliver fantastic ideas to an enormous range of clients. Recently we've been helping an international advertising agency develop a whole new model of trends and consumer behaviour; presenting to Mr Blair in Downing Street on public consultation; and carrying out important NPD and communications work for global brands like Coca-Cola and Reckitt Benckiser."
Castell began her career at Flamingo and was voted as one of ±±¾©Èü³µpk10's ‘Innovative young researchers' in 2002. She frequently writes and publishes papers and reports -- the most recent being "Getting the public's attention: communicating UK poverty", which was published this month by the Joseph Rowntree Association.