Jacob Franquart or Jacob Franckaert the Younger (1582/83 – 6 January 1651 (buried)) was a Flemish architect, painter, print artist, draftsman, military engineer and poet. He is known for his altarpieces and publications on contemporary Italian architecture. He was employed by the court of the Archdukes Albert and Isabella in Brussels as a painter and architect. He was responsible for the design of ephemeral decorations and structure for important occasions at the court such as funerals. As an architect and decorator, he introduced the Baroque in the buildings of the Habsburg Netherlands. His style is sometimes referred to as the Italo-Flemish style and became very popular in Flanders in the 17th century. Only a few paintings are attributed to him.

Franquart was born in Antwerp or possibly Brussels as the son of Jacob Franckaert the Elder and Michaela del Tronco. His date of birth is not known with certainty. He was likely born in 1582 or 1583. His father was a painter and draughtsman known for his religious subjects, landscapes and architectural scenes, who became a master in the Antwerp Guild of Saint Luke in 1571. A sister of Jacob the Younger named Suzanna was born around 1584. Jacob the Elder is still mentioned in Antwerp in 1585. His father took his family via Paris to Italy in 1591. In Naples, Jacob the Elder started a collaboration with Wenceslas Cobergher, a Flemish painter who had trained in Antwerp with Maerten de Vos. They executed several paintings for the city's churches.

Jacob the Elder moved with his family to Rome in 1594. Cobergher joined them and the two artists continued their collaboration. Four months after the death of his first wife, Cobergher married Suzanna Franckaert, the daughter of his collaborator, in Rome on 20 November 1599. At the time the Franquart family was registered in the register of the parish of San Lorenzo in Rome. In March 1601, the family was registered in the marriage register of the parish of San Lorenzo in Rome. It is difficult to discern in these works the contribution of either artist. Jacob started to study painting, likely with his father. In Rome, he had the opportunity to study the Antique and Renaissance architecture. He particularly admired the works of Michelangelo, Giacomo della Porta, Giacomo Barozzi da Vignola and Carlo Maderno.

Both parents of Jacob had died by September 1601 after which he lived with his sister Susanna and her husband Cobergher. At this time the Archdukes Albert and Isabella invited Cobergher to work for them at the court in Brussels causing him to leave Italy with his family. Jacob remained in Rome. At some point he got involved in a lawsuit regarding some stolen precious stones. The stones were rediscovered before the end of the trial. In the years 1607 and 1608, he was residing near the Santa Maria della Pace in Rome. Franquart returned to his homeland at the end of the trial and before the summer of 1611.

Some authors have stated that Franquart worked in the workshop of Rubens in Antwerp and that they were old friends. There is no documentary evidence for this. It is possible that the two artists got to know each other during their residence in Italy. Rubens' later purchase of Franquart's Premier Livre d'Architecture... (First book of Architecture) published in 1616 was possibly a sign of his respect for Franquart. Rubens may also have acquired the book purely for practical reasons as at that time he was carrying out renovations on his newly purchased home in Antwerp.

One month after the publication of Franquart's Premier Livre d'Architecture (Premier livre d'architecture de Iaques Francart : contenant diuerses inuentions de portes seruiables à tous ceux qui désirent bastir et pour sculpteurs, tailleurs de pieres, escriniers, massons et autres : en trois langues, in English First book of architecture of Jaques Francart : containing various inventions of doors useful to all those which wish to build and for sculptors, stone cutters, manufacturers of cases, masons and others: in three languages), he was asked to complete the Jesuit Church in Brussels (destroyed in 1812). Construction of the church had started in 1606 with Hendrik Hoeimaker as the building master. Franquart's involvement in this project launched his career as an architect. In 1620, he was put in charge of the construction of the Temple of the Augustinians in Brussels. In June 1621, he designed the funeral procession of the Archduke Albert. In 1629, he was commissioned to design the Beguinage Church in Mechelen. Franquart also rebuilt the Church of Our Lady by the Dijle in Mechelen, by adding a choir chapel and two side chapels as a continuation of the 16th-century choir. After Cobergher's death in 1632, Franquart was appointed engineer to the Spanish king. Franquart taught his niece Anna Francisca de Bruyns to paint. The leading Brussels sculptor Jerôme Duquesnoy (II) was appointed as his assistant.

He never married and died in Brussels where he was buried on 6 January 1651.

Franquart was a prolific artist who worked as an architect, painter, print designer, draftsman, military engineer and poet. His most important contributions are his publication on contemporary Italian architecture and introduction of the Baroque style in architecture in the Habsburg Netherlands.. He was employed by the court of the Archdukes Albert and Isabella in Brussels as a painter and architect. He was responsible for the design of ephemeral decorations and structure for important occasions at the court such as funerals. As an architect and decorator, he introduced early Baroque into the buildings of the Habsburg Netherlands. Only a few paintings are attributed to him. He was further active as a civil and military engineer.