Gen Sir Nicholas Carter's comments to the BBC came as the inquest into the death of Pte Cheryl James continued.
The Army was criticised recently after the deaths of three SAS trainees and a soldier who suffered unlawful physical punishment.
Sir Nicholas told Sunday Politics Wales: "It would be very difficult for those sorts of things to happen again."
Pte James from Llangollen, Denbighshire, was found dead with a gunshot wound in the Deepcut barracks in Surrey in 1995.
An initial inquest into her death in 1995 recorded an open verdict but that was overturned by the High Court, which ordered the new hearing, which is ongoing.
In another case, a coroner criticised the Army after three reservists died on a training exercise on one of the hottest days of 2013.
Coroner Louise Hunt ruled L/Cpl Edward Maher, L/Cpl Craig Roberts and Cpl James Dunsby died as a result of neglect on the 16-mile (25-km) march in the Brecon Beacons.
Pte Gavin Williams, 22, from Hengoed, Caerphilly, collapsed with heatstroke at Lucknow Barracks in Wiltshire in July 2006 and suffered heart failure.
It happened after he was forced to carry out a "beasting" - physical exercise as a punishment.
The coroner in his inquest said the Army's chain of command failed to prevent this unlawful practice being carried out.
Sir Nicholas said: "We've changed our culture, we've recently issued a new code of leadership, which is something I feel very strongly about.
"I would be surprised if it occurred again.  I'd never say it cannot happen, because of course it can, but we have put in place a lot of very different processes to ensure those sorts of things don't happen in the future."
The head of the Army says there has been a culture change in the forces after a number of deaths on duty.