Pierre Guillaume’s birth year varies between 1779 and 1807 in the original sources. However, family tradition, the oldest Manitoba censuses and the HBCo servant’s list of 1828 favor a date of birth around 1801 to 1803. With this date he would be in his early twenties and his wife, Josèphté, about sixteen when their eldest son, Edouard, was born May 17, 1823. According to her baptismal records at St. Francois Xavier, Manitoba, Josèphté was born in about 1807.
Sayer enlisted as a voyageur with the McTavish, McGillivray & Company on April 7, 1818. His inscription was registered by the notary public J.-G. Beek at Ste Anne, Bout de l'Isle at the western end of the Island of Montreal. He was hired to work in the areas controlled by the North West Company. The contract is preserved in the Archives Nationales du Quebec.
According to the Hudson Bay Archives, Pierre Guillaume worked for the North West Company at Cumberland House from 1818 to 1821, the year of the union of the North West and Hudson Bay Companies. From 1828-1829, he worked for the Hudson Bay Company as a Bowsman at Fort Pelly in the Swan River District and then stayed on as a Steersman from 1829-1832. In 1832, he was freed from his service in the Hudson Bay Company and moved to Grantown near the Red River Settlement.
When he enlisted with the Hudson Bay Company in 1828, he stated that he was 27 years old. This is shown on the HBCo Servants list of 1828 and gives him 1801 as the year of his birth.
On March 2, 1835, according to the St. Francois Xavier Catholic Church marriage records: Guillaume Sayer, son of John Sayer and an Ojibwe woman named Marguerite, married Josèphté Frobisher, age about 28 years according to her baptismal record of the same day, the daughter of Alexander Frobisher and Marguerite, a Cree woman.
Sayer had been trading to Norman Kittson in Pembina, North Dakota, who was in direct competition to the HBC. Sayer was accused of illegal trading of furs and was brought to trial in Upper Fort Garry on May 17, 1849 by the Court of Assiniboia. He was backed by Métis leader Louis Riel Sr.. During the trial, a crowd of armed Métis men gathered outside the courtroom, ready to support their Métis brother peacefully or by force if necessary. They demanded that Sayer be tried by a jury of his own choosing and that he be allowed to take fellow Métis into the court with him. Although being allowed to select a jury of his own, he was still found guilt by them. Judge Adam Thom, under immense pressure from the overwhelming number of armed Métis, levied no fine or punishment. With the cry, "Le commerce est libre! Le commerce est libre!" ("Free Trade! Free Trade!"), the HBC could no longer use the courts to enforce their monopoly on the settlers of Red River. In 1870 the trade monopoly was abolished and trade in the region was opened to any entrepreneur. The company relinquished its ownership of Rupert's Land under the Rupert's Land Act 1868 enacted by the Parliament of the newly formed Dominion of Canada.
According to the church records at St. Laurent, Manitoba, Pierre Guillaume died August 7, 1868 and was buried at St. Laurent the next day, August 8, 1868, at the age of 75 years. Father Laurent Simonet OMI, who started the Mission and became the first parish priest in 1864, officiated. The witnesses were Baptiste Lavallée and Pierre Chartrand.
- The various dates are found as follows:
- 1779 - appears in the Manitoba census of 1834 and in the update of 1835. However, this seems to be a copyist error as the name above his is missing its date and this is given to Pierre instead. This error is corrected in the formal census of 1835.
- 1793 - is the date given in the registry of his death and burial at St. Laurent, Manitoba.
- 1796 - is given on the census of 1849, the year that he was tried in court.
- 1801 - appears on the HBCo Servants List of 1828 in the HBCo archives.
- 1803 - is found on the censuses of 1833 and 1838. Pierre’s grandson, Alexander Henry Sayer, also stated that his grandfather was about 14 years old when he enlisted as a voyager in 1818.
- 1807 - comes from the censuses in 1835 and 1843.