Anna Rajecka was most likely born in 1754. Her father, Józef Rajecki, and her brother were also painters. Her first teacher was the pastellist Louis-François Marteau (c. 1715–1804) and she may have also studied under Marcello Bacciarelli (1731–1818), court painter to King Stanisław August. In around 1780, A. Rajecka was present at the royal court in Warsaw, where she produced drawings and pastel portraits.
She was the only woman to receive a royal stipend. In 1783, she travelled to Paris to continue her studies, producing copies for the king while residing in the Louvre galleries. At that time, Jacques-Louis David (1748–1825), Jean-Baptiste Greuze (1725–1805) and Élisabeth Vigée Le Brun (1755–1842) had opened studios for women at the Louvre. Although there is no direct evidence that A. Rajecka took lessons from any of them, she created works inspired by J.-B. Greuze’s style.

In 1788, A. Rajecka married the miniaturist Pierre-Marie Gault de Saint-Germain (1754–1842), to whom King Stanisław August also extended his patronage. However, the king did not approve of the couple’s planned trip to Italy that same year, nor of their plan to return together to Warsaw. At that time, he commissioned copies of portraits of prominent French figures for his collection. This task was entrusted, through his representative Filippo Mazzei (1730–1816), to J.-L. David (and his students), as well as to A. Rajecka, whose works were made under the supervision of the French painter. Out of all the works submitted, the king was most impressed by A. Rajecka’s pastels.

Amongst the pastels she sent to King Stanisław August was Girl with a Dove (1789–1790), believed to be a portrait of Princess Rozalia Lubomirska (1768–1794). The work has erotic undertones, depicting the woman reclining on a cushion with her breasts exposed and misty eyes. Similarly sensual is the undated pastel Sleeping Woman, offering a voyeuristic glimpse into an intimate scene. In Paris, A. Rajecka also painted portraits of Polish and French aristocrats. One of her most notable works is the Portrait of Ignacy Potocki (c. 1784), showcasing her soft, fluid style that creates a silky effect, along with her characteristic blue-brown colour palette. A. Rajecka also produced allegorical portraits symbolising the seasons, as exemplified by her pastel Summer (c. 1788).

The year 1791 marked the height of A. Rajecka’s career. She became the first Polish woman to exhibit at the Paris Salon, which had recently relaxed its rigid entry rules. From that point on, not only Academy members but also independent artists, including women, could display their works. A. Rajecka presented four pastel portraits at the Salon, though none are known to have survived today. She remained in Paris until 1792, when she stopped receiving her royal stipend. To escape the Revolution, A. Rajecka and her husband relocated to Clermont-Ferrand. While her husband pursued teaching and wrote on aesthetics, she continued painting portraits. Little is known about her later years, except for the fact that she gave birth to a son, Pierre-Xavier, in 1797. Eventually, the Gault de Saint-Germain returned to Paris, where A. Rajecka died in 1830.