FD won the retained account following a competitive pitch process.
The agency replaces Bell Pottinger Corporate and Financial, which had worked with the multinational defence and aerospace firm for six years.
The account will be led by FD's managing director of financial communications, Jonathon Brill, and supported by Billy Clegg and Christopher Clark in the financial and corporate teams.
The FD team will report to Charlotte Lambkin, group communications director.
The wide-ranging brief will see FD helping the firm strengthen its reputation amongst key stakeholders as the premier global defence and aerospace company.