Police will be on high alert as some 1,400 people are expected to attend a 10am service at Glasgow Cathedral, while thousands more will watch it live on a big screen in George Square.
Afterwards, Prince Charles and a number of foreign dignitaries, in the city for the Commonwealth Games, will lay wreaths at the cenotaph in George Square.
Those expected to attend include Gordon Campbell, the High Commissioner for Canada, Ranjan Mathai, the Indian High Commissioner, Governor-General of Australia Sir Peter Cosgrove and Sir Jerry Mateparae, Governor-General of New Zealand.
Kamalesh Sharma, the Commonwealth Secretary-General and leading figures from Scottish civic society will also attend.
The service in Glasgow is the first and largest of three First World War events being held as part of the UK Government's programme of centenary commemorations.
The others are at London's Westminster Abbey and Mons in Belgium.
Those taking part highlighted the importance of remembering the devastating impact of the First World War.
Between 1914 and 1918, the Great War claimed the lives of around 145,000 Scots, leaving many more thousands injured or disabled. Around 200,000 Glaswegian men volunteered to go to war, 18,000 of whom never returned.
Mr Salmond said: "No home, no school, no community in Scotland was left untouched by the Great War, which remains one of the most brutal conflicts the world has ever seen.
"As the curtain falls on 2014 Commonwealth Games, we acknowledge the countries of the Commonwealth we fought alongside during the Great War and it is fitting that this service in Glasgow Cathedral should focus on the contribution of these nations."
Mr Cameron said: "A hundred years ago today Britain entered the First World War and we are marking that centenary to honour those who served, to remember those who died, and to ensure that the lessons learnt live with us forever.
"It is right to remember the extraordinary sacrifice of a generation and we are all indebted to them because their most enduring legacy is our liberty."
Lord Provost of Glasgow, Sadie Docherty said she hoped people would be inspired over the coming four years to learn more about their own family and community's war history.
She said: "As a mother of a son, I have reflected on the fact that if I lived in Glasgow 100 years ago I would have been facing the prospect of my child going to war.
"Glaswegians must have been scared and worried about what it would mean to them and their family. As we now know it was a war that changed our world forever.
"And these fears and hopes aren't a historical past, with many parents still facing the same worries for their children in the military services today."
A spokeswoman for Police Scotland said: "As with any major event appropriate policing will be in place to ensure the security of all those involved."
Over the next few years, Scots will be asked to join in remembeance for a further seven events that had a particularly significant impact on Scotland.
These include the major battles of Gallipoli, Loos, Jutland and Arras, the Quintinshill rail disaster in which the Leith-based 7th Battalion Royal Scots Territorial Force lost 214 officers and men, the end of the war, and the loss of HMY Iolaire which struck rocks and sank half a mile from its destination of Stornoway with the loss of 204 men on New Year's Day in 1919.
Meanwhile, a wreath was flown from the UK's first operational military airbase in Montrose to a war memorial in Amiens, France, as part of the commemorations.