Sellier was appointed managing director of the Office des Habitations à Bon Marché (Office of Affordable Housing) of the Seine department when it was created in 1915, and dedicated himself to urban issues and public housing.
He moved to Suresnes that year, and would do much to improve the municipal facilities.

In 1918 Sellier and Marcel Poëte founded the École des hautes études urbaines (EHEU, School of Advanced Urban Studies) and the review La Vie Urbaine.

Sellier helped found the Union internationale des villes (International Union of Towns), of which he was vice president from 1920.

In 1925 he was one of the founders of the Union amicale des maires de banlieue (Friendly Union of Suburban Mayors).

Sellier became a role model for Social-Democratic city leaders in the inter-war period.

He aimed for a system in which efficient teams of specialists would regulate urban agglomérations to maximize the welfare and individual potential of the inhabitants.

These agglomérations would not necessarily reflect traditional administrative boundaries, but would be natural units for planning purposes.

He said, "The tentacular city is a fact.
Its advantages and disadvantages may be discussed, but it would be stupid to deny it and reckless to hinder its social role.

He saw the old administrative structure of Paris and its surrounding communes as an outdated obstacle to healthy evolution of the overall urban area, in which unregulated capitalist expansion would inevitably cause social evils.

Sellier proposed a ring of garden cities surrounding Paris.

Over the years Selliers views evolved from emphasizing local political responsibility to an approach based more on social sciences and cost effectiveness.

Sellier wanted Suresnes to become a city at whose gates "the prospective inhabitant ceases to be a worker and becomes once more a man."

He became hugely popular as he transformed Suresnes into a model of modernist and rationalist urban planning.

As soon as he took office as mayor of Suresnes in 1919 Sellier began to establish a system of social services with a special emphasis on the health of children.

One of his first steps was to restructure the colonie de vacances through which children from the city were given vacations of eight or more weeks with country families in the Nièvre.

The children would be freed from the collective discipline of the city, "one of the major causes of mental exhaustion among children in our great cities."

They would gain a living link to the countryside, a sort of adopted birthplace.

Sellier organized health protection from infancy, created institutions for education at all ages, built many public facilities and was innovative in providing housing that was comfortable and hygienic.

He inspired the creation of fifteen garden cities between 1920 and 1945: Boulogne-Billancourt, Champigny-sur-Marne, Charenton-le-Pont, Châtenay-Malabry, Drancy, Drancy Cité de la Muette, Gennevilliers, Les Lilas, Maisons-Alfort, Le Plessis-Robinson, Le Pré-Saint-Gervais/Pantin, Stains, Vanves and Vitry-sur-Seine.

In 1937 Sellier and Poëte founded the Fédération Internationale de l’habitation et de l’urbanisme (International Federation of Housing and Urban Planning).
Sellier was appointed managing director of the Office des Habitations à Bon Marché (Office of Affordable Housing) of the Seine department when it was created in 1915, and dedicated himself to urban issues and public housing. He moved to Suresnes that year, and would do much to improve the municipal facilities.
In 1918 Sellier and Marcel Poëte founded the École des hautes études urbaines (EHEU, School of Advanced Urban Studies) and the review La Vie Urbaine.
Sellier helped found the Union internationale des villes (International Union of Towns), of which he was vice president from 1920.
In 1925 he was one of the founders of the Union amicale des maires de banlieue (Friendly Union of Suburban Mayors).
Sellier became a role model for Social-Democratic city leaders in the inter-war period.
He aimed for a system in which efficient teams of specialists would regulate urban agglomérations to maximize the welfare and individual potential of the inhabitants.
These agglomérations would not necessarily reflect traditional administrative boundaries, but would be natural units for planning purposes.
He said, "The tentacular city is a fact. Its advantages and disadvantages may be discussed, but it would be stupid to deny it and reckless to hinder its social role.
He saw the old administrative structure of Paris and its surrounding communes as an outdated obstacle to healthy evolution of the overall urban area, in which unregulated capitalist expansion would inevitably cause social evils.
Sellier proposed a ring of garden cities surrounding Paris.
Over the years Selliers views evolved from emphasizing local political responsibility to an approach based more on social sciences and cost effectiveness.
Sellier wanted Suresnes to become a city at whose gates "the prospective inhabitant ceases to be a worker and becomes once more a man."
He became hugely popular as he transformed Suresnes into a model of modernist and rationalist urban planning.
As soon as he took office as mayor of Suresnes in 1919 Sellier began to establish a system of social services with a special emphasis on the health of children.
One of his first steps was to restructure the colonie de vacances through which children from the city were given vacations of eight or more weeks with country families in the Nièvre. 
The children would be freed from the collective discipline of the city, "one of the major causes of mental exhaustion among children in our great cities." 
They would gain a living link to the countryside, a sort of adopted birthplace.
Sellier organized health protection from infancy, created institutions for education at all ages, built many public facilities and was innovative in providing housing that was comfortable and hygienic.
He inspired the creation of fifteen garden cities between 1920 and 1945: Boulogne-Billancourt, Champigny-sur-Marne, Charenton-le-Pont, Châtenay-Malabry, Drancy, Drancy Cité de la Muette, Gennevilliers, Les Lilas, Maisons-Alfort, Le Plessis-Robinson, Le Pré-Saint-Gervais/Pantin, Stains, Vanves and Vitry-sur-Seine.
In 1937 Sellier and Poëte founded the Fédération Internationale de l’habitation et de l’urbanisme (International Federation of Housing and Urban Planning).
Henri Sellier