[2] As a youngster, Hartmann had stints with Portsmouth and then at Swindon Town where he was eventually released at the end of the 2009–10 season.

In the 2010–11 United Football League mid-season transfer window, he joined Loyola and then scored his first goal in a 2–1 defeat to the Philippine Air Force.

[7] On 15 October 2011, Hartmann scored five goals in a 15–1 win over newcomer Team Socceroo in the 2011–12 United Football Cup.

[9] On 10 June 2016, Geylang International announced on their Facebook page that they signed Hartmann from Global, making him the first Filipino to play in the S. League.

[11] Geyland decided not to renew Hartmann's contract due to budgetary constraints[12] and clubs from Thailand, Malaysia, and the Philippines has expressed interest to sign him.

[23] He made his first appearance for the under-23 national team in the 3–1 loss against Vietnam in the opening match of the 2011 Southeast Asian Games.