Stilwell, who will join Seven in January 2012, will be responsible for growing the agency's existing B2B portfolio as well as spearheading the company's ambitious UK and international growth strategy.
Sean King, Seven CEO, said: "Rachael brings 17 years' experience of building Haymarket's B2B brands including Media Week, Campaign, Marketing, PR Week and Brand Republic. She is going to be a huge asset for Seven as we look to grow our business in the UK and globally.
"The B2B market is a major opportunity for us and we have been looking for the right person to lead our growth in this sector for some time, so I am incredibly excited about Rachael coming on board.
"Her extensive knowledge and expertise in building up cross-platform brands is something all of our clients are looking for."
Stilwell said: "I am delighted to be joining Seven at such an exciting time in its development. Their content innovation is inspiring and their ambition for success is infectious.
"I can't wait to be part of this award-winning team."