[1] His brother, Dr. Thomas McCrae, became a professor of medicine at Johns Hopkins Medical School in Baltimore and close associate of Sir William Osler.

His sister Geills married James Kilgour, a justice of the Court of King's Bench of Manitoba, and moved to Winnipeg.

[3] Among his papers in the John McCrae House in Guelph is a letter he wrote on July 18, 1893, to Laura Kains while he trained as an artilleryman at Tête-de-Pont barracks, today's Fort Frontenac, in Kingston, Ontario.

"I have a manservant ... Quite a nobby place it is, in fact ... My windows look right out across the bay, and are just near the water's edge; there is a good deal of shipping at present in the port; and the river looks very pretty."

In 1910, he accompanied Lord Grey, the Governor General of Canada, on a canoe trip to Hudson Bay to serve as expedition physician.

In December 1899, McCrae volunteered for active service in South Africa as a Lieutenant in 'D' Battery, Canadian Field Artillery during the Second Boer War.

They arrived in Cape Town in February 1900, and fought in skirmishes in the Orange Free State and the Transvaal, including the Carnarvon Expedition and at the Battle of Belfast in August 1900.

[15] McCrae's friend and former militia member, Lt. Alexis Helmer,[16] was killed in the battle, and his burial inspired the poem, "In Flanders Fields", which was written on May 3, 1915.

For eight months the hospital operated in Durbar tents (donated by the Begum of Bhopal and shipped from India), but after suffering from storms, floods, and frosts it was moved in February 1916 into the old Jesuit College in Boulogne-sur-Mer.

'"[17] "In Flanders Fields" first appeared anonymously in Punch on December 8, 1915,[18] but in the index to that year, McCrae was named as the author (misspelt as McCree).

[19] The verses swiftly became one of the most popular poems of the war, used in countless fund-raising campaigns and frequently translated (a Latin version begins In agro belgico...).

"In Flanders Fields" was also extensively printed in the United States, whose government was contemplating joining the war, alongside a 'reply' by R. W. Lillard ("...

McCrae, now "a household name, albeit a frequently misspelt one",[21] regarded his sudden fame with some amusement, wishing that "they would get to printing 'In F.F.'

He was buried the following day in the Commonwealth War Graves Commission section of Wimereux Cemetery,[24] just a couple of kilometres up the coast from Boulogne, with full military honours.

Though various legends have developed as to the inspiration for the poem, the most commonly held belief is that McCrae wrote "In Flanders Fields" on May 3, 1915, the day after presiding over the funeral and burial of his friend Lieutenant Alexis Helmer, who had been killed during the Second Battle of Ypres.

The poem was written as he sat upon the back of a medical field ambulance near an advance dressing post at Essex Farm, just north of Ypres.

The poppy, which was a central feature of the poem, grew in great numbers in the spoiled earth of the battlefields and cemeteries of Flanders.

An article by Veteran's Administration Canada provides this account:[28]The day before he wrote his famous poem, one of McCrae's closest friends was killed in the fighting and buried in a makeshift grave with a simple wooden cross.

Wild poppies were already beginning to bloom between the crosses marking the many graves.The Canadian government has placed a memorial to John McCrae that features "In Flanders Fields" at the site of the dressing station which sits beside the Commonwealth War Graves Commission's Essex Farm Cemetery.

The statue shows the destruction of the battlefield and, at his feet, the poppies which are a symbol of Remembrance of World War I and all armed conflict since.