Captain Millar is from Shrewsbury, Massachusetts. He graduated in 2015 from the University of North Carolina with a Bachelor of Arts in Peace, War and Defense. In August of 2019, he graduated OCS and commissioned as a Second Lieutenant. After graduating from The Basic School and the Marine Artillery Officer Basic Course he reported for duty to Battery O, 5th Battalion, 14th Marines, Naval Weapons Station Seal Beach, CA.
Second Lieutenant Millar immediately joined Battery G, 2nd Battalion, 11th Marines at Integrated Training Exercise 1-21 in Twentynine Palms, CA where he completed his drill and Annual Training for the year as their Fire Direction Officer. In January 2021, Second Lieutenant Millar was activated with Battery G, 2nd Battalion, 11th Marines for a Professional Development Tour. While there, he acted as the Battery Fire Direction Officer and deployed as part of Battalion Landing Team 3/5 on the 31st Marine Expeditionary Unit, supporting six training exercises to include the Joint Force Coalition Exercise Talisman Sabre. He was promoted to First Lieutenant in August 2021.
Upon completion of his Professional Development Tour, First Lieutenant Millar rejoined Battery O, 5/14 in January 2022. While assigned to 5th Battalion, 14th Marines, he served as a Battery Fire Support Officer, completing his Annual Training as a part of 1st Battalion, 11th Marines FIREX. As the Battalion Fire Support Officer, First Lieutenant Millar supported 1st Battalion, 25th Marines during Integrated Training Exercise 4-23. In September 2023, First Lieutenant Millar became the Battery Executive Officer and acting Commanding Officer of Battery O during a transition period. He relinquished Battery Command in October 2023 and resumed his role as the Battery Executive Officer. In January 2024, he was promoted to Captain. He completed his Annual Training as the Battery Executive Officer in support of 2nd Battalion, 24th Marines during Integrated Training Exercise 4-24.
Captain Millar activated in October 2024 for UDP Infantry Battalion 25.1 as the Company G Fire Support Officer with 2nd Battalion, 23rd Marines. While there, he supported the Artillery Relocation Training Program (ARTP) in Hokkaido, Japan as well as the Korean Marine Exchange Program (KMEP) in Pohang, South Korea.
Upon returning from the UDP, Captain Millar served as the 5th Battalion, 14th Marines S4, planning the logistical support for the artillery battalion through March FIREX and Integrated Training Exercise 3-26. In July 2026, Captain Millar assumed Battery Command of Battery N, 5th battalion, 14th Marines.