He spoke to trainers, force protection and medics, as well as members of teams that manage logistics, administration support, communication and intelligence.
"When I spoke with an Iraqi General who was overseeing the training we were providing his troops, already battle-hardened from the current campaign in Mosul, he was very clear that the New Zealand and Australian training was critical to their future success - not only in liberating Mosul but the longer term challenges of stabilising ground won back from ISIS".
"Another clear take away from meeting some of the Iraqi troops on the ground and their leadership in Baghdad is how the mix of our professional soldiering and understated humility was really connecting with the Iraqis and is a key ingredient in the success of the training and adoption of the techniques in theatre.
"There is a genuine level of trust and respect being built up".
"With ISIS in full retreat, New Zealand is playing its part in this critical mission," he said.
Mr Muller is chairman of Parliament's Foreign Affairs, Defence and Trade Select Committee.
Kiwi soldiers in Iraq
- 106 Kiwi soldiers in joint taskforce with Australia assisting Iraqi forces
- The taskforce has trained 22,000 Iraqi soldiers trained 2015
- 60,000 square kilometres have been liberated
- 1.7 million Iraqis have returned to their homes
- 250,000 children are now back at school.