Talyllyn Junction was a railway junction located 4 mi (6.4 km) east of Brecon, Powys, opened in 1869. The junction was triangular, with north, east and west chords, station platforms being sited at the western junction and also, until 1878, at the eastern junction. The Junction took its name from the adjacent tiny hamlet.

The junction was created where the Brecon and Merthyr Railway from the south met the Mid-Wales Railway from the north-east. Both railways were to serve Brecon, and to achieve this the latter had running powers over the former from Talyllyn into Brecon. The eastern spur of the triangle permitted through running from South Wales to mid-Wales and also to Hereford.

The northern side of the triangle followed the course of the 1816 Hay Railway, a tram-road worked by horses connecting the town of Hay with the Brecknock and Abergavenny Canal at Brecon. At the western end lay a tunnel which required widening and deepening for use by standard gauge trains.

Talyllyn Junction is often quoted as a defining feature of the Great Western Railway in Wales, namely its inheritance of junctions in unlikely and inconvenient locations. Other examples are Moat Lane Junction, Dovey Junction, Afon Wen and Barmouth Junction (renamed Morfa Mawddach in 1960).

All the railways at Talyllyn Junction were closed to passengers in 1962.

• Mitchell, Vic; Smith, Keith (2003). Brecon to Newport. Middleton Press. figs. 14-19. ISBN 9781904474166. OCLC 828666902.
• Mitchell, Vic; Smith, Keith (2007). Brecon to Newtown. West Sussex: Middleton Press. figs. 10-17. ISBN 9781906008062. OCLC 288983659.

Preceding station		Disused railways		Following station
Groesffordd Halt Line and station closed		Cambrian Railways Mid-Wales Railway		Llangorse Lake Halt Line and station closed
		Brecon and Merthyr Tydfil Junction Railway Northern section		Talybont-on-Usk Line and station closed