She said leading the Tories in Holyrood - the job which she took on in November 2011 - had been the "privilege of my life".
But as she formally resigned as leader, Ms Davidson - who had campaigned for Remain in the 2016 European referendum - cited the "conflict" she had felt over Brexit.
She also said that "work has always come first" over the past eight years, but the arrival of her son Finn last October meant she now wants to make a "different choice".
With elections looming, she said the prospect of "spending hundreds of hours away from my home and family now fills me with dread".
And she added: "That is no way to lead."
She said: "I fear that having tried to be a good leader over the years, I have proved a poor daughter, sister, partner and friend. The party and my work has always come first, often at the expense of commitments to loved ones.
"The arrival of my son means I now make a different choice."
Ms Davidson clashed with Boris Johnson during the Brexit referendum, and her resignation came just a day after the Prime Minister announced he will temporarily suspend Parliament in the run-up to the UK's EU departure date of October 31.
But she stressed it was "both professional and personal" changes that had prompted her decision to quit.