The route towards Aylesbury opened in stages between 1868 and 1899: The Great Central Railway (GCR) decided to build a main line called the London Extension from Annesley Junction north of Nottingham to London via the Metropolitan Railway.

In 1903 the line between Harrow and Canfield Place (near Finchley Road) was built, thus bypassing this part of the Metropolitan tracks.

The line beyond Aylesbury Vale Parkway is currently closed to almost all passenger services: the Metropolitan line service north of Aylesbury to Verney Junction and Brill was withdrawn in 1936 as London Transport (LT) wanted to focus more closely on London.

In 1925, four rail electrification reached Rickmansworth and Watford, and the Metropolitan Railway planned to electrify the line as far as Aylesbury by 1935.

The original intention to electrify further is evidenced by the colour light signalling which was fully installed as far as Aylesbury and by platform extensions up to Stoke Mandeville.

The mainline services north of Aylesbury (via Woodford Halse, Rugby and Loughborough to Nottingham Victoria and beyond) were withdrawn in 1966 as the Great Central Main Line was seen by Dr Beeching as a duplicate of the Midland Main Line.

Beyond Amersham, the line returns to Network Rail control and runs northwest to Aylesbury, following the A413 road.

London Underground own the track and co-run on the line between Harrow on the Hill and the property boundary north of Amersham.

As a result, all Chiltern trains must be fitted with the tripcock braking system to run on Underground lines.

Large increases in 2010-11 in some stations are mainly due to the introduction of Oyster Cards on the National Rail Network.