| Nationality: | Brazilian |
| Birth Name: | Gregori I. Warchavchik |
| Birth Date: | April 2, 1896 |
| Birth Place: | Odessa, Russian Empire (now Ukraine) |
| Death Place: | São Paulo, Brazil |
| Practice: | Warchavchik |
| Significant Buildings: | The First Modern House in Brazil (1927-28) |
Gregori I. Warchavchik (April 2, 1896 – July 27, 1972) was a Jewish-Brazilian architect.
Warchavchik was born in Odessa, Ukraine which was then a part of the Russian Empire. He began his architectural studies at Odessa University and moved to Rome in 1918 to study at the Accademia di Belle Arti di Roma, the Superior Institute of Fine Arts. He graduated in 1920 and worked as an assistant to the architect Marcello Piacentini (1881-1960), later known as the main proponent of Fascist architecture in Italy.
Warchavchik arrived in Brazil in 1923. He married Mina Klabin in 1927, daughter of a prominent industrialist in São Paulo, and became a naturalized Brazilian. His house in São Paulo, Casa da Rua Santa Cruz, built between 1927 and 1928, is considered the first modernist residence in Brazil. He designed the Lasar Segall Museum in São Paulo that opened in 1967. In 1930 he and Lucio Costa established a joint architecture studio in Rio de Janeiro, and one of the designers in the studio between 1932 and 1936 was the then young architectural student, Oscar Niemeyer.
Warchavchik died in São Paulo in 1972.