Medium Transport
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Confusion
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Environment - Non Weather Related; Procedure; Human Factors
Departing ZZZ and assigned the ZZZZZX departure. The departure was thoroughly briefed before flight. All waypoints checked. We went as far as setting up the engine out procedure in the secondary flight plan. After takeoff the PF began the departure. The aircraft was cleaned up; accelerated; and hand-flown. A busy time immediately after departure. Within one minute after departure and after completing the after takeoff checklist I looked at my primary display and noticed our flight path was roughly one mile west and one mile south of the left-hand initial curve of the ZZZZZ Departure. It was visual conditions and I believe the PF got distracted by maintaining visual with the terrain outside during the initial steep climbout and not focusing closely enough on the departure course line. I did not catch the deviation initially with the workload and all happening within a couple minutes. There was never any issue with terrain or traffic. ATC stated after this initial departure climb that we were off our course; and I acknowledged this. Both myself the PNF; and the PF have flown very little in the last 3 months. I believe for the PF that this was his first leg in a few months. For myself; I've had 3 legs in the last 3.5 months. There is something to be said for a small lack of proficiency that this created; and not catching the error with a faster scan or recognition.  Another factor was the PF wanting to get the feel of the plane again and to wanting to hand-fly a busy DP in mountainous terrain.
Pilot reported a track heading deviation and cited lack of flying as a contributing factor.