Gillis Coignet, Congnet or Quiniet was a Flemish Renaissance painter, who was strongly influenced by the Italian style. He painted historical and mythological subjects of an easel size, but was more successful in landscapes, in candlelight subjects, and moonlight. He was a Lutheran, which probably influenced his moves from Antwerp to Amsterdam and then Hamburg. He spent most of the 1560s in Italy.

Gillis was born in Antwerp, the son of Gillis the Elder, a scientific instrument maker, and Brigitta Anthonis. In the certification book of the city of Antwerp of 1579 he claimed to be 37 years old, in that of 1586 he claimed to be 43, thus he was born ca. 1542 and, if his statements are correct, he was born between April and September of that year. He had the misfortune to be born with a large hairy mole in his face, hence his nickname Gillis met de Vlek (Gillis with the Spot). According to the Guildbooks of the Guild of St. Luke, Gillis was apprenticed to Lambrecht Wenslyns. Van Mander's claim that he stayed with the art dealer Anthony Palerme for some time is correct. The latter testified in 1586 that Gillis had been boarding with him when his parents were still alive (i.e. before 1562). In 1561 Gillis was admitted to the Guild of St. Luke as a Master.

In the second half of the 1560s he journeyed through Italy, where he visited inter al. Florence, Rome, Naples and Sicily. According to the Florentine Accademio del Disegno, Giulio Cognietta fiamingo P[ictor] was present at their meeting of 16 January 1568. In Terni (Umbria) he worked with a painter called Stello on frescoes and an altar in fresco style. According to Van Mander, Stello was Flemish, Nicole Dacos identifies this Stello as a member of the family of painters Stellaert from Mechelen. Both painters are mentioned in a document as members of a group of decorators who embellished the salon of the Villa d'Este under the supervision of Frederico Zuccaro, they also worked on an embossed grotesque in the Palazzo Giocosi. Apparently Gillis also worked for Francesco de' Medici.

After 1570 he returned to Antwerp where he employed a number of apprentices. In July 1571 the painter Willem vanden Bosch wrote to the Duke of Alba that Gillis would like to enter the service of the Duke.

Gillis was married to Magdalena de Kempeneer, but it is uncertain whether he married her before or after his Italian journey. They had only one child Juliana (?- about 1616).

At the end of the 1570s they lived in the house De hove van de Jonge Voetboog, which belonged to the Guild of St-Joris (St. George). In March 1580 he and his wife bought the lifelong usufruct of the house for 750 guilders on the condition that the Guild members could use the bowling green at any time. The house stood in the Schuttershofstraat and had a rent value of 40 guilders.

For the monthly quotisation, a special tax levied to pay for defence against the Spaniards, Gillis Coignet's family was taxed at 2 guilders 10 stivers indicating that Gillis enjoyed affluent circumstances. At that time Gillis was considered to be a Martinist (i.e. a Lutheran).

In 1581 Gillis became a member of the Armenbus of the Guild of St. Luke. The Armenbus was founded in 1538, following the example of other trades, and was formed to support the members who by sickness or accident were unable to support their families or whose relatives were too poor to pay for the burial service. After joining the Armenbus there was a waiting period before the benefits could be enjoyed. The Armenbus was chaired by two 'busmeesters', in the first year one was 'medebusmeester' (deputy chairman) and in the succeeding year became 'hoofdbusmeester' (chairman). In 1582, one year after joining the Armenbus Gillis became mede-busmeester, in the following year he became hoofdbusmeester with Philip Galle, the engraver, as medebusmeester. This same year Gillis seems to have persuaded a number of his relatives to become members of the Armenbus, including his brothers the physician Jacob and the court mathematician Michiel together with their wives.

In 1584 Gillis became Dean of the Guild of St. Luke, a post he would continue to perform during and shortly after the siege by the Spaniards. It therefore can be no surprise that doubts about his religion and his behaviour were raised after the Reconciliation. In 1586, however, Anthony Palerme and Jan van de Kerckhove testified that Gillis had behaved himself "with all modesty and peacefulness". Gillis also testified on behalf of other Guild members, e.g. he testified together with Philip Galle and Gerard de Jode that Marten van Valckenborch and his son-in-law Henrick van Steenwijck were citizens of the town.

It appears that Gillis had no intention to leave the city at that time. He paid his dues to the Guild for 1585–86, and on 3 October 1585 he and Philips Galle, the new Dean, examined the accounts of the Guild. Apparently some difficulties arose, a dispute occurred and a conciliatory meeting with the elders (= previous deans) was held on 26 October 1585. His last appearance in the Guildbooks dates back to Ascension Day 1586, when it became apparent that the accounts he and Ambrosius Vrancken had drawn up did not balance.

In the Spring of 1586 Gillis sold the usufruct of the house to Hendrik Jennen. A note from Philip Galle, written after 4 September 1586, makes clear that Gillis had left town.

Gillis went to Amsterdam, where he became a citizen in 1589. According to van Mander he was a successful painter in Amsterdam, and influenced the art scene in that city considerably. Van Mander also asserts that it was Gillis Coignet who persuaded Hans Vredeman de Vries to come to Amsterdam.

On 6 April 1588 he was a representative for the Lutheran community of Amsterdam. On 15 March 1590 he had a dispute with the Calvinist painter Adriaan Conflans. It is not clear whether their religious beliefs had anything to do with this dispute, but it is not impossible as the relations between Lutherans and Calvinists in the Amsterdam at that time were very bad indeed.

About 1593-94 Gillis went to Hamburg, "because of his religion or something else" according to van Mander, and he is last mentioned in Amsterdam on 21 January 1593, when he was a witness at a baptism. His painting Lottery on the Rusland, painted in Amsterdam, is dated May 1593, while The Last Supper was painted in Hamburg dated 1595. Gillis died in Hamburg on 27 October 1599 and was buried in the Jacobskirche.

His daughter Juliana married Philips van der Veken; she died before or during 1616. Her husband tried, as the executor of her will, to recover the money which her father had lent to the city of Antwerp.