Castro, a Spanish national, will join the online auction powerhouse as director of government relations in Brussels on 1 January.
She will be responsible for public affairs and represent the Silicon Valley-headquartered firm's interests with European institutions.
Castro, who said she was headhunted for the role, will leave her current job - also based in Brussels - after almost eight years.
During that time, the fast- food company has faced major criticism over its alleged role in soaring obesity levels, as illustrated in the 2004 film Super Size Me.
Castro helped develop McDonald's ‘worldwide nutrition labelling' initiative. The principal lobbying agency with which she has worked is Brussels-based Strategic Communications.
At eBay, which runs payment system PayPal and internet-voice firm Sykpe, Castro will report to Dr Anja Bundschuh, director of government relations for Europe. Bundschuh is based in Bern, Switzerland, where eBay has its European HQ.
In Brussels, Castro joins European policy manager Claudia Breure and Annalisa Barbagallo, PayPal's director of government relations for Europe, who will continue to report to Bundschuh.
The company also has government relations staff in its German, French and UK offices. It does not retain a pan-European public affairs consultancy, preferring to work with agencies in individual markets.
Its UK head of public affairs is Alasdair McGowan, who joined last year (PRWeek, 13 Oct 2005). The company continues to use Bell Pottinger Public Affairs for UK lobbying (PRWeek, 18 Jun 2004).
At McDonald's, Castro reports to Europe V-P of corporate relations Karen Van Bergen. Castro said the company is yet to decide how she will be replaced.