Most of the deep level stations opened in the first phase between Finsbury Park and Hammersmith were built to a design by Leslie Green.
This consisted of two-storey steel-framed buildings faced with dark oxblood red glazed terracotta blocks, with wide semi-circular windows on the upper floor.
Earl's Court station was built with a red brick building by Harry Ford, with semicircular windows on the second level and embedded names of the railways which operated through the station.
This replaced a wooden hut building and is listed as Grade II.

Extensions of the Piccadilly line towards the west and north in the 1930s had new stations designed by the Adams, Holden & Pearson architectural practice of the Underground, with Charles Holden the main designer.
These designs were inspired by modern architecture seen in a 1930 trip to a number of European Countries.

Several stations on the western extension, which were opened by the District Railway, were to be reconstructed.
The new designs were to use brick, concrete and glass, composing of simple geometrical shapes, such as cylinders and rectangles.
The first prototype station was Sudbury Town station, which had the main structure a brick cuboid box, with tall windows above the entrances, then topped by a concrete slab roof.
This was then replicated across many other station prototypes.
Some stations were designed by delegated architects of Holden due to workload, such as Stanley Heaps and Felix Lander.
Other stations had their original stations kept.
South Ealing was an anomaly, where a temporary wooden station ticket hall was constructed when the line was quadrupled.
A modern station was provided in the 1980s.
The northern extension stations also were part of the design schemes undertaken by this practice.
Southgate was distinctively different, with a round base followed by a cylindrical panel of clerestory windows, topped by an illuminative feature with a bronze ball.
The ticket halls had passimeters, which functioned as free-standing ticket booths.
Most of them went out of use post World War II, while some have been converted for retail use.
Many of these Holden-designed stations are listed buildings.
Oakwood, Southgate, and Arnos Grove were a few of the early receivers of listed status, in 1971.

Stations in Central London were modernised with a variety of changes.
Green Park received a new shelter at the southern entrance; Piccadilly Circus had its ticket hall moved below street level.
Both of these features were designed by Holden, with the latter station ticket hall added with artwork commemorating Frank Pick in 2016.
Green Park was built with a new entrance at a corner of Devonshire House, which has Portland Stone clad steel frames.
It features Graeco Roman details, and is Grade II listed.

Stations on the northern extension had particular biscuit (square) tiles on platform walls, with different freize colours at each station.
A few stations like Southgate and Bounds Green have art deco uplighters on escalators and the lower landings.
Floodlighting was used considerably to provide a spacious ambience.
Ventilation ducts were by the platforms walls, sealed with bronze art deco style grilles.
Oakwood was built with a concrete canopy with rooflights and cylindrical light fittings, designed by Heaps.
Older stations such as Caledonian Road have platform tilings with arcs clad along the tube platforms, with each arc spaced 11–12 ft (3.4–3.7 m) apart.
On the platform end, geometrical tiles were squeezed into a defined horizontal region; varying among stations.
Arc lighting was complemented with incandescent lamps to illuminate the platforms.
Signage decorations present spelt out the station name, with their font size 15 in (38 cm) high.
Most of the deep level stations opened in the first phase between Finsbury Park and Hammersmith were built to a design by Leslie Green. This consisted of two-storey steel-framed buildings faced with dark oxblood red glazed terracotta blocks, with wide semi-circular windows on the upper floor. Earl's Court station was built with a red brick building by Harry Ford, with semicircular windows on the second level and embedded names of the railways which operated through the station. This replaced a wooden hut building and is listed as Grade II.
Extensions of the Piccadilly line towards the west and north in the 1930s had new stations designed by the Adams, Holden & Pearson architectural practice of the Underground, with Charles Holden the main designer. These designs were inspired by modern architecture seen in a 1930 trip to a number of European Countries.
Several stations on the western extension, which were opened by the District Railway, were to be reconstructed. The new designs were to use brick, concrete and glass, composing of simple geometrical shapes, such as cylinders and rectangles. The first prototype station was Sudbury Town station, which had the main structure a brick cuboid box, with tall windows above the entrances, then topped by a concrete slab roof. This was then replicated across many other station prototypes. Some stations were designed by delegated architects of Holden due to workload, such as Stanley Heaps and Felix Lander. Other stations had their original stations kept. South Ealing was an anomaly, where a temporary wooden station ticket hall was constructed when the line was quadrupled. A modern station was provided in the 1980s. The northern extension stations also were part of the design schemes undertaken by this practice. Southgate was distinctively different, with a round base followed by a cylindrical panel of clerestory windows, topped by an illuminative feature with a bronze ball. The ticket halls had passimeters, which functioned as free-standing ticket booths. Most of them went out of use post World War II, while some have been converted for retail use. Many of these Holden-designed stations are listed buildings. Oakwood, Southgate, and Arnos Grove were a few of the early receivers of listed status, in 1971.
Stations in Central London were modernised with a variety of changes. Green Park received a new shelter at the southern entrance; Piccadilly Circus had its ticket hall moved below street level. Both of these features were designed by Holden, with the latter station ticket hall added with artwork commemorating Frank Pick in 2016. Green Park was built with a new entrance at a corner of Devonshire House, which has Portland Stone clad steel frames. It features Graeco Roman details, and is Grade II listed.
Stations on the northern extension had particular biscuit (square) tiles on platform walls, with different freize colours at each station. A few stations like Southgate and Bounds Green have art deco uplighters on escalators and the lower landings. Floodlighting was used considerably to provide a spacious ambience. Ventilation ducts were by the platforms walls, sealed with bronze art deco style grilles. Oakwood was built with a concrete canopy with rooflights and cylindrical light fittings, designed by Heaps. Older stations such as Caledonian Road have platform tilings with arcs clad along the tube platforms, with each arc spaced 11–12 ft (3.4–3.7 m) apart. On the platform end, geometrical tiles were squeezed into a defined horizontal region; varying among stations. Arc lighting was complemented with incandescent lamps to illuminate the platforms. Signage decorations present spelt out the station name, with their font size 15 in (38 cm) high.
Piccadilly line