In March 2022, Herdman signed a contract with
Whitecaps FC 2. He made his professional debut on 26 March against
Houston Dynamo 2. In November 2023, he signed an extension with the team for the 2024 season. While with Whitecaps 2, he served as team captain for a spell. After participating in the 2024 pre-season with the
Vancouver Whitecaps first team, he signed a short-term loan agreement with them ahead of their
CONCACAF Champions Cup Round One first leg against
Tigres UANL, but was an unused substitute in the match. He signed addition short term loans on March 1 and April 19. On April 20, he made his
Major League Soccer debut, in a substitute appearance against
Seattle Sounders FC. In September 2024, Herdman was loaned to
Canadian Premier League club
Cavalry FC for the remainder of the 2024 season. Upon his move to Cavalry, he was converted to a left winger role, from his typical central attacking roles. He made his debut on September 15 against
Atlético Ottawa. He scored his first goal and added his first assist, in his first start for Cavalry, on October 5 against
Pacific FC. After the 2024 season, Whitecaps 2 declined his option for 2025. In January 2025, he signed a permanent contract with Cavalry. In August 2025, Herdman was loaned to
Vancouver FC for the remainder of the season. ==International career==