Grounds' departure, which is understood to have been with immediate effect, was confirmed in a statement by the charity, which did not offer an explanation of why he left.
His departure follows the resignation with immediate effect of CEO Gavin Grant, who departed in February citing health concerns.
Grounds was promoted to deputy CEO from director of marketing and communications in July and subsequently led a radical review of its agency line-up as part of a ten-year strategy plan leading up to its 200th anniversary in 2023.
According to the charity's statement its trustees "are very grateful for the contribution he has made to the RSPCA and to animals and would like to wish him well for the future".
The statement includes this message from Grounds to staff: "I’m extremely proud to have worked with you all and to have seen the wonderful work of the Society’s staff, volunteers and supporters first hand. Your commitment to the welfare of animals is humbling. I wish you all the very best."