Its southern terminus begins as a junction with the M13 Highway in Hillcrest, KwaZulu-Natal. The R103 begins as the Old Main Road and leaves Hillcrest in a roughly north-west direction and enters Cato Ridge from the east. In Cato Ridge, the road crosses the N3 at the 53 exit and then follows the south side of the N3 before recrossing the freeway again at Camperdown. It follows the N3 towards the outskirts of Pietermaritzburg crisscrossing the freeway several times. It enters Scottsville, Pietermaritzburg from the south-east where at a T-junction it co-signs with the R56 and heads north through the suburb. The R56 breaks of to the east and the R103 leaves Scottsville crossing the Msunduzi River and heading north-west into the Pietermaritzburg CBD as its main road. Leaving the CBD, it continues until around the suburb of Athlone. The road resumes following the N3 in a north-westerly direction passing through Hilton before reaching the outskirts of Howick. Crossing under the N3 it enters the suburbs of Howick and circles the town as an easterly ring road before reaching the N3 Junction 103 in the north close to the Midmar Dam. Leaving the N3, it heads in a north-westerly direction passing through Lions River, Ligetton West and Zenzani before turning north outside the town of Nottingham Road and heads towards the southern end of the town of Mooi River. Leaving Mooi River, the road heads north-east then after a short distance heads north-west eventually crossing the Boesmans River and enter Estcourt from the east. It heads north through Estcourt as its main road before leaving the town north-west. It then passes through Frere crossing the Bloukrans River before intersecting the R74 at a t-junction. Co-signed with R74 it heads north-east and enters Colensofrom the south where its splits from the R74 which heads east. Bypassing the town to the west it crosses the Tugela River heading north-west. Passing through Roosboom it then turns north-east and enters the outskirts of Ladysmith where it interchanges with N11 before bypassing the town to its west. The R103 turns west, just south of the Windsor Dam and continues until it joins N3 at the Tugela Toll Plaza. Co-signed with the N3 it heads north-west where it passes through Van Reenen and leaves Kwazulu-Natal and enters the Free State.
Free State
Leaving Van Reenen, it heads west still co-signed with the N3 before heading north-west when crossing the Wilge River. It enters the outskirts of Harrismith from the south where it interchanges with the eastern terminus of the N5 National Route. It heads north as an eastern bypass of the town. It leaves Harrismith in a north-westerly direction before entering Warden from the south after a long distance. The N3/R103 bypasses to the town's west leaving it northwards and after a short distance the two roads split again and the R103 becomes its own road, heading in a north-easterly direction to meet theR34 west of Vrede. It now heads north-west, co-signed with the R34 for a short distance before the R34 becomes its own road westwards. Continuing north-west, the R103 passes Cornelia to its east before entering Villiers from the south where it co-signs with the N3 at its intersection with the R26, Just north of the N3 Villiers Toll Plaza.
Continuing north-west past the town of Villiers, as the N3, it crosses the Vaal River into the Mpumalanga province. At junction 5, it interchanges with the R54/R51 and continues north-west. At junction 28, the interchange leads to Grootvlei in the east, but the N3/R103 continues in a northerly direction where it crosses into the Gauteng province at the Suikerbosrant River, where another tollgate is located.
Continuing north it crosses the R23 before bypassing Heidelberg to the east. North of Heidelberg at junction 70, the freeway meets the R23 again. At this off-ramp, the R103 leaves the N3 freeway and co-signs briefly with the R23 eastwards up to the next junction, where the R103 becomes its own road and begins to follow the N3 north-west as the Old Heidelberg-Alberton Road, crossing the R550 soon after. Near Vosloorus, it interchanges with the M35 Road and M43/R21 Road and in Roodekop, the M53. The R103 briefly changes direction at a t-junction in Roodekop, south of Wadeville, Germiston, where it becomes part of the Nederveen Highway and is cosigned with the R554 westwards towards Alberton Central. At the N3 Highway crossing, the Nederveen Highway changes its name to Heidelberg Road. At the Swartkoppies Road junction, the R554 becomes the road to the left and the R103 becomes the road to the right towards the Alberton Central Business District and Johannesburg. At the junction with the N12 Southern Bypass just after Alberton Central, The R103 ends and the road continuing northwards to Johannesburg Central is designated as the M31 Road of Johannesburg.
