Jan Rejchl was the youngest offspring of local builder and architect Václav Rejchl Sr. After graduating from a secondary school in Hradec Králové, he went to the Italian front at the age of eighteen. While his older brother Václav learnt architecture from the older generation of architects at the Czech Technical University in Prague, such as Josef Schulz, Jan Koula and Adolf Liebscher, Jan learnt from the new generation in 1919–1924. His most important teacher was Antonín Engel. After graduation, Jan Rejchl went to study at Josef Gočár’s special school of architecture at the Academy of Fine Arts in Prague, and from July 1926 to February 1927, he was on paid internship in Josef Gočár’s studio. Subsequently, he participated in the competition for the crematorium and funeral hall in Strašnice, eventually won by Alois Mezera. Rejchl won later, in the competition for the savings bank in Slaný, which was also Mezera’s birthplace . The savings bank was built between 1928 and 1931 and it represents Gočár’s impact on Jan Rejchl. His style was manifested in the purist composition of materials and the use of unplastered brickwork. In 1927, a competition was announced for a new building of the State Technical School in Hradec Králové, which was won by Oldřich Tyl, but the project was eventually carried out by Jan Rejchl for some unclear reasons. Rejchl simplified the original progressive project in the international style and used more traditional forms. The turn of the 1920s and 1930s meant the greatest workload for Jan Rejchl. Together with his brother, Václav Rejchl Jr., he designed the train station building in Hradec Králové, combining monumental and progressive forms. They also participated in important competitions for elementary and secondary schools, eventually designed by Josef Gočár. Then Jan Rejchl also designed the building of the glass institute, originally panelled with frosted glass, the building of the National Bank of Czechoslovakia, the completion and courtyard extension of the Municipal Savings Bank in Velké náměstí Square, and many other projects. At that time, Jan Rejchl focused not only on public buildings, but also on monuments and memorials (for example, he designed of the monument to Bedřich Smetana together with Vincenc Makovský, the memorial to the Silesian revolt in Hůrka near Opava together with Josef Wagner, and monuments to Josef Ladislav Pospíšil in Hradec Králové, and Jan Theodor Held in Třebechovice together with Josef Škoda) and tourist architecture: between 1933 and 1934, he designed the Panorama chalet on Šerlich Mountain in the Orlické Mountains and the chalet on Čihák Hill.
In 1934, Jan Rejchl defended his dissertation on the Municipal Savings Bank and became a doctor of technical sciences. After World War II, he designed several buildings as an independent architect, for example, the telegraph exchange building below the brewery and the cooperative laundry in the Labská kotlina housing estate. In the summer of 1948, he was asked by Ladislav Machoň to become director of the newly established design institute in Hradec Králové, which brought together all the nationalized architectural studios. In the institute, Rejchl collaborated with architects František Steiner, Václav Rohlíček, and his son, Milan Rejchl. In 1958, Jan and Milan Rejchl participated in the competition for the U Soutoku housing estate that Oldřich Liska, Věra Machoninová, František Čermák and Gustav Paul participated in as well. In the 1970s, the father and son designed a civic centre with a museum and library in Lázně Bělohrad, which was not eventually built. Together with Václav Rohlíček, Jan Rejchl designed the interiors of the ROH civic centre in Ústí nad Labem, designed by local architect Jaroslav Lácha. Together with Karel Schmied, he worked on the extension of the school for tanners designed by Josef Gočár. Other projects in the mid-1950s included the boarding house of the TEPNA factory in Náchod and the boarding school of the LINA factory in Jaroměř, designed together with Václav Placák.
Between 1947 and 1950, Jan Rejchl taught architecture at the Faculty of Architecture History of the Technical University in Brno – the preserved preparations and copies of slides prove that he put an emphasis on thorough knowledge of classical architecture.
In 1953, he published one of the most remarkable theoretical books, Harmonie architektonického díla (The Harmony of Architectural Work), fairly openly criticizing socialist realist architecture and functionalist architecture, the scientific principles of which he never liked. In the book, he wrote that “the effort to amaze the viewer [that] makes [the architect] use any architectural means to make the first impression and say everything in one breath” is decadent. As for the architecture of the interwar avant-garde, Rejchl wrote that “mechanically articulated façades bore us with their monotony” .
In 1975, Jan Rejchl retired; he died at the age sixty eight ten years later.
 The rivalry between Rejchl and Mezera was dealt with by the contemporary press in a profile article on Rejchl: [b. a.], Ing. Jan Rejchl, Úspěch: Magazín snaživých, 1934, vol. IV., no. 3–4, pp. 123–125.
 Jan Rejchl; Hana Stašková, Harmonie architektonického díla. Dílčí úkol výzkumu Architektonická kompozice, Prague 1953.
Municipal Savings Bank in Slaný
Dissecting and pathological-anatomical pavilion and hospital administrative building in the hospital complex in Hradec Králové
Extension and modification of the Municipal Savings Bank in Hradec Králové, 33 and 800 Velké náměstí Square
Mr. Seifert’s villa in Hradec Králové, 819 Hradební Street
Restaurant pavilion in the Jiráskovy sady Park in Hradec Králové, no. 237
Extension of the Chamber of Commerce, Trade and Industry in Hradec Králové, 695 Škroupova Street
Residential building in Hradec Králové, 944 Průmyslová Street
Automatic telephone exchange in Hradec Králové, 954 ČSA Avenue
Laundry and dry-cleaning in Hradec Králové, 960 Labská kotlina housing estate
Jih Elementary School in Hradec Králové
Bezruč Elementary School in Hradec Králové (with Z. Gabriel)
- , Úspěch: Magazín snaživých, 1934, p. 123–125
- Jan Rejchl, Hana Stašková, Harmonie architektonického díla. Dílčí úkol výzkumu Architektonická kompozice, Praha 1953
- Otakar Nový, Československý architekt: Časopis Svazu architektů ČSR, 1974, p. 2
- František Toman, Architekt, 1999, p. 71–72
Pavel Vlček (ed.), Encyklopedie architektů, stavitelů, zedníků a kameníků v Čechách, Praha 2004, s. 542–543.
- Jakub Potůček, Hradec Králové: Architektura a urbanismus 1895-2009, Hradec Králové 2009
- Ladislav Zikmund-Lender, Tři generace architektů: Václav st., Václav ml., Jan a Milan Rejchlovi, Hradec Králové 2012
- Ladislav Zikmund-Lender, Zprávy památkové péče, 2013, p. 154–156
- Ladislav Zikmund-Lender, Východočeské listy historické, 2015, p. 157–175