The head of the armed forces, Air Chief Marshal Sir Jock Stirrup, is to give evidence to the Iraq Inquiry.
He will face questions about military operations in Iraq from 2006, when he took over as Chief of the Defence Staff (CDS), to the draw down of British troops last year.
He will also be asked about a previous role as deputy chief of defence staff (equipment) at the time of the invasion in 2003 amid criticisms that vital kit failed to reach troops on the front line.
The inquiry will also hear from his predecessor as CDS, General Lord Walker of Aldringham, who took over in May 2003, shortly after the invasion, having previously been head of the Army.
On Sunday, former international development secretary Clare Short claimed that Gordon Brown was "marginalised" by Tony Blair throughout most of the build-up to the invasion.
Ms Short, who gives evidence to the inquiry on Tuesday, said Mr Brown had feared that Mr Blair would use a quick victory over Saddam Hussein to strengthen his political position at home and remove him from the Treasury.