"He has my wholehearted support, as well as the support of the wider Scottish Conservative family."
Ms Davidson, the leader of the Scottish Conservatives, is also gay.
Angela Eagle, shadow first secretary of state and shadow business secretary, is the most senior gay Labour politician.
Mr Mundell has three children and has been an MP since 2005. At the 2015 general election, he was the only Tory MP elected in Scotland.
Lord Smith was the country's first openly gay cabinet minister during Tony Blair's time as Prime Minister.
How David Mundell came out as gay
New Year, new start! I have already set out my political priorities for the year and now I am setting out my personal one. Having taken one of the most important decisions of my life and resolved to come out publically as gay in 2016, I just want to get on with it, and now, just like that, I have said it. How can it be both so easy and so hard to say a few short words?
In the end, it took just a couple of taps on a keyboard, yet at some points, in my mind, it was going to be harder than standing for election, speaking in the House of Commons or being cross-examined on television. I still cannot fully rationalise such feelings, but I know they are not uncommon, particularly in men of my age. Of course, everybody who gets to this point, has had their own journey. I have certainly been on mine - conflicting emotions, of doubts and fears, but ultimately positive and uplifting, with an unstoppable direction of travel. Over time, I came to understand that, for me, the only way to be truly happy on a personal level is to acknowledge in public as well as in private, who I am.
I so admire the many people, young and old, who are doing this every day, uncertain of the reaction. I have been very fortunate and couldn’t have had more love and support from my family and friends. However, making this public is something I have had to do myself. I don’t know what the wider reaction will be, but I know it’s the right thing for me to do.
Other than the intensely personal and positive difference it makes to me, and the way I can live my life, my hope is that my coming out doesn’t change anything else about how I go about my work or how people treat me. Gender and sexuality should make no difference whether you are a Cabinet Minister or in any other walk of life and I hope that I can, in my own way, reinforce that message.
How the internet reacted
John McTernan, former political adviser to Tony Blair:
Ruth Davidson, leader of the Scottish Conservatives:
SNP MP Stewart McDonald:
Source: http://telegraph.feedsportal.com/c/32726/f/579309/s/4cd56ae1/sc/13/l/0L0Stelegraph0O0Cnews0Cpolitics0Cconservative0C120A97320A0CCabinet0Eminister0EDavid0EMundell0Ecomes0Eout0Eas0Egay0Bhtml/story01.htm