The ranges of the service buildings are set out irregularly around 3 courtyards. The E courtyard is the mews and is surrounded by stables, coach houses, and workshops, whilst the central and W courtyards have buildings associated with domestic activities. The exterior walls of the complex are of ashlar and have a greater degree of architectural embellishment than the interior walls.
The W courtyard is entered through an impressive portal on the N side which adjoins the main house. The angles of the portal are chamfered and parapets rise from a string course. A raised frieze in the centre has a square traceried panel bearing a shield with a lion. Four-centred chamfered archway. To the R is a short wall behind which is a small room, with small 2-light window with continuous hoodmould. To the L, a wall with decorated crenellated parapets forms the boundary to the W courtyard. This joins the square tower of the brew house. The squat 2-stage tower has stepped diagonal buttresses and pronounced crenellated parapets on a corbel table decorated with trefoils. Wide ventilation openings to 1st floor, 8 lights to each face containing Gothic tracery: Trefoiled lancets to N, lattice design with quatrefoils to E and diamond and quatrefoil design to W. A short octagonal tourelle at the NW angle rises above the main parapets, and has cross-shaped ventilation slits to alternating faces.
The exterior boundary continues to the S with the E gable end of the laundry, which projects slightly beyond the brew house. This has an ornate stepped chimney breast with shields in relief in square panels, above and below a traceried lattice frieze. The stack has 2 octagonal shafts. A string course flanking the chimney breast rises over shields in square panels. From the S angle of the chimney breasts, a boundary wall dog legs round further ranges including the boiler house. The wall has parapets on a corbel table, and a setback buttress and large finial where it changes angle. To the L is a 4-centred arched door under a square hoodmould leading into the gun room.
Further L is the wide entrance to the mews courtyard: Two high octagonal piers with buttress to 4 sides, surmounted by lions couchant. To the L (E) of the entrance are the exterior walls of the stables and coach houses. Immediately L of the entrance is the wide gable end of a stable block which has moulded verges with pendant finials and a large finial on the apex. The E wall of this stable and the N wall of the coach house are continuous. The former is 4-bay and the latter 3-bay, each bay divided by angle buttresses surmounted by finials, and with plain parapets on a corbel table. Adjoining to the L is the N wall of a highly ornate building forming the NE corner of the complex; it contained the bridle room, stables, and the grooms' accommodation over. It is of 2 storeys and an attic; the N side is 5-bay with angle buttresses rising to high octagonal finials. Crenellated parapets which rise over 2 dormer windows to the 2nd and 4th bays, each containing a 2-light window with Y-tracery. High octagonal cupolas rise from the apex of each dormer with narrow open lancets. A similar but larger cupola is corbelled out from the W gable apex of the building. The E gable end has a stepped gable, large apex finial and short square angle piers corbelled out at parapet level. It is dominated by a large oriel attic window supported on a 2-stage pier. Moulded arched braces spring outwards from the top of the pier to support the window, with a recessed traceried panel in the spandrels. The attic window has a cinquefoiled-head under an ogee hoodmould with head end bosses. The oriel bay has diagonally-set flanking piers with finials. Flanking the pier are 2-light windows with shallow pointed heads under square hoodmoulds. The attic storey of the S wall is visible from the exterior and is in a similar style to the N wall; ornate crenellated parapets with attic dormers to 2nd and 4th bays with flanking octagonal pinnacles with domed traceried caps, and with pendant finials. This building is joined to the S by a single storey stable range at right angles. Its exterior E face is similar to the stables to the N; five bays divided by angle buttresses which rise to octagonal finials, with plain parapets on a corbel table. The S gable end has diagonal buttresses and a large central stepped buttress which rises as an octagonal pinnacle with decorated traceried cap. From the SW angle runs a short length of wall with an entrance containing late C20 double planked gates.
From the SW gates, the wall turns to the W where it forms the boundary to the mews courtyard. It is of plain ashlar with corbel table decorated with arched frieze, supporting plain parapets. The bays are separated by buttresses, and where the angle changes, the parapets are raised and decorated with shields. Some sections are in poor condition, with later buttressing. The wall turns to the NW for a short distance and joins the SE angle of a range which was used as a squash court in the early C20. The exterior S side is of 7 bays separated by angle buttresses which rise as octagonal pinnacles with traceried domed caps. Each bay has a 3-light window with lancet heads under a square hoodmould. Parapets decorated with raised triangles, on a corbel table. Pointed Gothic doorway to W gable end with several orders of mouldings and hoodmould with head bosses, containing double planked doors. Set in a recessed panel with pronounced frieze of pendant finials to top. The doorway is flanked by similar but smaller recessed panels. Finial to front of gable apex. From the SW angle of the building, a low retaining wall with parapets runs S and joins the garden terrace walls of Margam Castle. From the NW angle of the building, the boundary wall runs N for 1 bay and then W for 3 bays. In the angle is a large tripartite pier set at an angle and containing a niche for a seat (heavily covered in vegetation). This wall joins the SE angle of the house.
The courtyard to the W has a flagstone floor and is entered through the N portal. The main house forms its W boundary. Against the N boundary wall is a low lean-to with late C20 openings, now an aviary. To the E is the W face of the brew house which includes the entrance; a panelled door under a 4-centred chamfered arch approached by stone steps. To its R is the gable end of the laundry, of rubble stone with dressed stone to the upper half. The doorway is to the R, approached by stone steps, with double planked doors under a 4-centred arch. To its L is a large square window opening, infilled with rubble, with a small enclosure in front. L of the laundry is the projecting end wall of the single-storey bakehouse, with hipped roof and large 3-light mullioned window with quarries. On the S side of the courtyard is a rubble stone dividing wall with doorways at each end which lead into a further small courtyard, with kitchen window of main house to W, boundary wall to S and larder to E. The R doorway has a heavy stone lintel and the L doorway also leads into a short passage which provides access to the central courtyard.
The large central courtyard is bounded to the S by the former squash court. Its rear wall is plain with a C20 door inserted. A short length of boundary wall is to the W with a doorway with steps leading down into the W courtyard. To the N is a U-shaped range of single storey buildings of coursed rubble stone, including laundry and bakehouse. The laundry to the N has 2 large 3-light mullioned windows with diamond quarries. The brew house tower rises behind. On the E side is the access to the boiler house, a 4-centred arched chamfered stone doorway containing a planked door. Beyond is the laundry maids' sitting room. This has a wide gable to the L and contains a doorway to the L with heavy chamfered stone lintel and wide 3-light window to the R with heavy dressings and mullions, possibly enlarged. Similar window to S gable end. From its SE corner is the rear wall of the workshops, now containing a late C20 through-passage. On the W side of the U-shaped range is the bakehouse and larder. The end of the bakehouse is to the R with a hipped roof and a hipped half-dormer containing a 3-light window with transom. The range continues to the L at a lower level with a 2-light window.
The mews courtyard to the E is paved in cobbles. Single storey range to W side containing gun room and workshops. The gun room has a gable to the N end containing a 2-lancet window under a square hoodmould and with a diagonally-set finial. Rubble stone below window, ashlar above. Square corbelled stack to L angle rising to an octagonal shaft. The range continues to the L with a small 2-lancet window and then a planked door to gun room, both rising to the eaves. Three planked doors to the workshops to the L, all with louvres above. The central door now opens onto a through-passage to the central courtyard, and to its R is a 2-light mullioned window with flat head. Wide gabled bay to S end, ashlar above rubble stone, with tablet attached to apex bearing a shield with chevrons. Wide opening offset to L with chamfered jambs, now containing door and glazing for a gift shop. The N side of the courtyard is bounded by the stables, bridle room and coach houses. The tall ornate range in the NE corner is plain rubble below attic level, the doors and windows with flat heads in dressed surrounds. Two planked doors to the ground floor are flanked by 2-light windows with lancet heads. Further door and window to far R. The stable range at right angles forming the E boundary of the courtyard is now converted to toilets. The W wall is rendered and contains late C20 doors flanked by high-level windows. Original flat headed, chamfered doorway to L with planked door. Running W from the ornate NE building is the single storey L-shaped range containing coach house and stables. Three bays with double planked doors under a continuous wooden lintel, the R bay infilled with a late C20 door and window. To the L is a wide gabled bay with 2 cart-shed openings with dressed jambs, now glazed. Vent in gable apex in stone surround. The W wall of the coach house has no openings, but further N is the entrance into the adjoining stable. Planked door with boarded overlight under flat chamfered stone lintel, flanked by 2-light windows with lancet heads. The S side of the courtyard is the boundary wall, against which is the low remains of a former range, now a raised flower bed.