Charlotta (Lotten) Sofia Rönquist was admitted to the Royal Academy of Fine Arts in 1884 and studied there until 1890. Among her fellow students at the Academy were Gottfried Kallstenius, Gerda Roosval-Kallstenius, Anton Genberg, Anshelm Schultzberg, Carl Johansson, Hilma af Klint, Hanna Pauli, Ida Gisiko-Spärck, Carl Flodman, among others. During the summer of 1886, Rönquist participated in an artists' excursion to Kungsör, led by the academy professor and artist Per Daniel Holm. She was accompanied on the trip by several of the aforementioned artist friends.

In the late 1890s, until the early 1900s, Rönquist shared a studio with Hilma af Klint and Alma Arnell in the so-called "Atelier Building" owned by the Royal Academy of Fine Arts. It was located on Hamngatan at the corner of Kungsträdgården. The "Atelier Building" was the cultural centre of Stockholm at the time. Also in the same building were Blanchs Cafe and Blanchs Art Salon, where the battle was fought between the Royal Academy of Fine Arts' conventional art view and the Artists' Association's French-inspired opposition movement.

After her time at the Academy, she studied in France. In 1892, she was in the artists' colony at Gréz-sur-Loing. After her time in France, Rönquist travelled to Italy where she worked and studied for five years. She painted portraits in miniature, interiors, landscapes, and still lifes.

During her last fifteen years, she executed several monumental paintings for hotels, castles, and churches. In the Grand Hotel in Stockholm, a number of large paintings are preserved in the so-called Winter Garden.

Rönquist was a member of the Swedish Artists' Association, participating in its exhibitions about ten times from 1886. She also took part in many other exhibitions, including the Artists' Association's exhibitions in southern Sweden.

After her early death at the age of 48, a memorial exhibition was held at Salong Joël in Stockholm in 1912.