David Mansfield, current chairman of Rajar is set to assume the joint role of chairman and chief executive, while a suitable successor to de la Bedoyere is found.
De la Bedoyere was previously managing director at Associated Newspapers' Evening Standard and, prior to that, was advertising director at The Mail on Sunday.
Rajar collects and processes radio diaries from respondents. Those radio diaries form the basis of the official measurement and profile of commercial and BBC radio stations in the UK. Commercial radio stations also use Rajar figures when trading radio airtime.
De la Bedoyere was known as one of the more colourful Rajar chief executives.
When she joined in 2003, the chief executive famously locked horns with the former editor of The Sun, Kelvin MacKenzie, then chairman and chief executive of The Wireless Group, who launched a £66m court action against Rajar over what it claimed were lost revenues.
A spokesman for the RSPCA confirmed de la Bedoyere would be joining the organisation at the end of the month.
The latest Rajar audience measurement figures for the first quarter of 2010 will be released tomorrow (13 May).
Since its humble beginning in 1824, the RSPCA has annual running costs of £82m, which are funded exclusively by voluntary donations and legacies.
The RSPCA became one of the first charities to use augmented reality in its marketing activity last October, as part of its Big Stop Circus push.