Macdonald joins B-M in mid-September as an MD and is Elliott's first senior hire since joining this year from Trimedia Communications (PRWeek, 7 January).
Her brief is to bring in new business in the aerospace and defence, financial services, IT, property and chemicals sectors.
Elliott said Macdonald's recruitment was 'a serious statement of our intention to develop the public affairs business significantly'. He added that B-M planned to hire three more staff - two at MD or director level - by the end of the year.
Macdonald has been at BPPA for almost two years. She previously acted as special adviser to ex-secretary of state for Scotland Helen Liddell.
B-M corporate and PA director Peter Digger quit for Upstream in May.