Aerated wetlands (AW) are normally used for high oxygen demand situations and were proven optimal for nitrification. However, denitrification remains a concern in AWs especially due to unfavorable oxygen concentrations and lack of biodegradable organic matter (OM). In this study, a 350 m2 aerated horizontal subsurface flow constructed wetland (HSSF CW) treating the effluent of a municipal wastewater treatment plant, was tested in a high hydraulic loading rate situation (0.69 m3.m−2.d−1, 12 h hydraulic retention time), in combination with external carbon dosing to promote denitrification. Forced bed aeration (FBA™) allowed to independently aerate three equally sized zones along the flow direction, and was controlled by a Dissolved Oxygen (DO) sensor in each zone. Zone 1 was destined for nitrification (DO = 2–3 mg.O2.L−1), zone 2 for denitrification (no aeration) with the addition of a carbon source (Brenntaplus VP-1), and zone 3 was again aerated (DO = 2–3 mg.O2.L−1) to degrade any residual OM. Four different carbon dosages (COD/N 0, 2.0, 3.5 and 4.0) were applied at the start of zone 2, based on online measured nitrate data. The results revealed that nitrification remained optimal (±100%) throughout the experiment despite the lower water temperature (10–15 °C). Total nitrogen (TN) removal increased from 23 to 59% as the COD/N ratio increased from 0 to 4. However, the COD removal efficiency remained moderate during initial dosing (21 and 18% for COD/N = 0 and 2, respectively) and further decreased with higher carbon dosing (no removal for COD/N = 4.0). The outcomes of this study can be helpful for implementing carbon dosing to enhance nitrate removal in full-scale AWs used for tertiary treatment.