Thea Leonhard was a designer and interior decorator.

Thea Leonhard was born in Helsinki in 1925. She and her two sisters were brought to Sweden by their mother following the end of World War Two. From 1947 to 1949 she attended Konstfackskolan (now Konstfack, college of arts, crafts, and design) in Stockholm. At that time the influential interior designers Carl-Axel Acking and Lena Larsson were members of school’s teaching staff. This post-war period was an important time in the sphere of Swedish interior design, particularly given the call for high-quality interiors for official buildings.

Thea Leonhard collaborated professionally with several of the leading architects of the time, including Sven Markelius and the founders of AOS arkitekter AB, Magnus Ahlgren, Torbjörn Olsson, and Sven Silow. In 1954 she provided the interior design for Renhornet mountain farm in Jämtland, which had been created by the architect Birger Jonsson. Thea Leonhard’s longest-lasting working partnership was with the married architects Charles-Edouard and Léonie Geisendorf. Some of the premises that Thea Leonhard provided the interior design for include Villa Ranängen in 1951, and Hushålls- och sömnadsskolan (domestic sciences and sewing school) in 1960, located in Kungsholmen, Stockholm (later St. Görans gymnasium). Following Charles-Edouard Geisendorf’s appointment as professor at Eidgenössische Technische Hochschule (ETH) architectural school in Zürich, Thea Leonhard continued working with him. She moved to Zürich in the mid-1960s, working not only with Geisendorf but also with Etienne Grosjean, a professor of ergonomics at ETH.

Thea Leonhard displayed her work at several well-known exhibitions. She submitted her chair design called Flamingo to H55, an exhibit organised in 1955 by Svenska Slöjdföreningen and held in Helsingborg. The chair now forms part of the Stockholm National museum collections. In 1957 she was involved in Från helhet till detalj, an exhibition to celebrate Carl-Axel Acking organised by the National museum on the occasion of his departure from Konstfack. In 1960 and 1966 Thea Leonhard was one of the active members of the HI group – comprising master crafters and interior designers who sought to revitalise Swedish furniture design.

Thea Leonhard also gained international renown. Her work was presented in the American design magazine Interiors in 1965, whilst two of her chairs were included in New Furniture 6, a survey volume from 1962 which covered the HI group exhibition.

Thea Leonhard died in Switzerland in 1972.