The worst shooting on US soil, at Pulse nightclub in Orlando, Florida, in the early hours of Sunday, also saw a further 53 people injured.
Omar Mateen burst into the lesbian, gay, bisexual, and transgender (LGBT) venue and opened fire while armed with an assault rifle and handgun before taking hostages.
He was shot by police at the nightclub after a three-hour stand-off.
Two vigils will be held in Scotland in memory of those killed in the tragedy.
Organisers of Glasgow Stands With Pulse Orlando said: “With the tragic news of the shooting at the gay club Pulse in Orlando, we’re holding a vigil in George Square to show our support for LGBTQ people worldwide, and to provide a space for us to mourn with our community.
“This attack is a reflection of the violence LGBTQ people face daily, not just in the US but across the world, and this violence feels personal for many of us.
“This was a hate crime against our community, and an extension of the messages that we hear daily that we should not be visible, we should not be out, we should not exist.”
The statement ended: “The inclusive support of our whole community, and of the wider Glasgow community, is vital as we mourn the loss of so many lives, and continue to fight the bigotry that allows such attacks to happen in the first place.”
A similar event, “Edinburgh Stands With Orlando”, is set to take place in the capital’s St Andrew Square on Wednesday.
The rainbow Pride flag, a symbol of the lesbian, gay, bisexual, and transgender (LGBT) community, will also fly over the Scottish government’s headquarters
First Minister Nicola Sturgeon tweeted: “The #Pride flag will fly at half mast over @scotgov HQ today in memory of those whose lives were taken in #Orlando. #lovewins”.
Glasgow City Council has also flown the rainbow flag at half-mast over the City Chambers in George Square, with Lord Provost Sade Docherty saying: “Our thoughts and prayers are with all those affected by the terrible atrocity.”
After news of the shooting, which injured 53 others, Ms Sturgeon said that “no words can convey my horror and sadness”.
Scottish Conservative leader Ruth Davidson, who proposed to her partner Jennifer Wilson in May, wrote: “News from Orlando is shocking - people from all around the world stand with the LGBTQ community today.”
Scottish Labour leader Kezia Dugdale, who confirmed she was gay two months ago, tweeted: “Scenes from Orlando utterly heart-breaking. The very freedom to love and dance attacked in the most brutal, destructive and senseless way.”
The so-called Islamic State (IS) group has since claimed responsibility for the attack.
In the aftermath of the shooting, communities around the world have been organising vigils to remembers those who were killed and injured.