Early career Growing up, Halloran played for the Colorado Thunderbirds and Colorado Rampage 16U AAA in the
Tier 1 Elite Hockey League (T1EHL). He made his U15 Midget Minor debut with the Thunderbirds during the 2012–13 season and moved to Colorado with his mother for his first two seasons in the T1EHL. He advanced to the Colorado Rampage 18U AAA during the 2014–15 season where he recorded 26 points in 24 games Halloran declined and chose to play with the
Trail Smoke Eaters in the
British Columbia Hockey League (BCHL) where he led the team with 45 points in 53 regular-season games. When speaking of his decision to play at
Colorado College, he admitted that his years playing with the Thunderbirds and Rampage influenced his choice. Later that month, he was named NCHC Rookie of the Week after scoring three of the team's five goals over a two-game weekend against Boston College and New Hampshire. Halloran ended the season with a selection to the 2016–17 NCHC's Academic All-Conference Team and tied for sixth on the team with five goals in 29 games. His 45 points placed him third overall in the conference and 15th in the country while also earning him the Thayer Tutt Award as team MVP and M.B. Hopper Award as the team's leading scorer. As a result of his play, Halloran won back-to-back NCHC Player of the Month accolades for December and January. was named a
Hobey Baker Award nominee, and became the first Tiger since 2012 to be selected as a
Second-team All-America. After his successful season, Tigers coach
Mike Haviland estimated that 10 to 15 professional teams took an interest in Halloran and said "we [the team] didn’t know if he’d come back for that junior year." It was later revealed that Halloran had played through a torn labrum and required surgery to remove a bone spur during the offseason. Leading up to his third year at Colorado College, Halloran was selected for the NCHC Preseason All-Conference Team as voted on by local and select media members. He was also praised by
Air Force Falcons coach
Frank Serratore who speculated that he would end his collegiate career early to pursue a professional one. This would never come to fruition as he struggled at the beginning of the season and underwent a second surgery in January which cut his season short. Halloran announced he would rejoin the Tigers for his fourth and final season and said "I definitely feel like a new person. My hip was really bothering me, and it was a tough decision to get it fixed. But ultimately, I believe it was the right one. I’m flying now." As a result of their outstanding play, both Wilkie and Halloran were nominated for the 2020 Hobey Baker Award. Due to the
COVID-19 pandemic, his senior season was cut short and he moved his classes online so he could return home. When asked what his first purchase would be with his first check, Halloran said he would open a savings account. With the season shortened due to the pandemic, Halloran made just 15 appearances, collecting 8 points, in his lone season with the Reign. As a free agent, Halloran embarked on a European career by splitting the following
2021–22 season between
Finnish club,
SaiPa of the
Liiga and Swedish club,
Örebro HK of the SHL. In showing his offensive acumen, Halloran as a free agent opted to continue in the SHL, securing a one-year contract with
Timrå IK on May 18, 2022. In the
2022–23 season, Halloran contributed offensively for Timrå in adding 7 goals and 15 points in 27 appearances. On January 24, 2023, Halloran opted to leave the club and sign for the remainder of the season with Swedish second tier club, Modo Hockey of the HockeyAllsvenskan. ==Career statistics==