Unite's Scottish secretary Pat Rafferty said: "We thank Kezia for the work she has done to contribute to the Scottish labour movement and the party in Scotland, and wish her very well in all she does in the future".
She pitched Scottish Labour as a boring version of the nationalists, suggesting reforms which would pull Scotland further apart from the Union but stopping short of the exciting proposition of independence.
"Kezia became Scottish leader at one of the most hard times in the history of the Scottish Labour party and the party's revival is now fully under way, with six new MPs and many more to come".
Political commentators in Scotland have described how Dugdale has faced criticism from left-wing party members and had in the past been critical of Corbyn.
Ms Dugdale, who is leaving with immediate effect, told the BBC she had devoted "every waking moment of my life" to improving Labour's fortunes in Scotland and that the party now ready for someone else to take it on the next stage of its journey.
In her letter to Scottish Labour Party chairwoman Linda Stewart, she stated: "Too often our leaders leave in a crisis, with scores to settle".
Chair of the Edinburgh Southern Constituency Labour Party and Labour Hame editor Duncan Hothersall said he was proud to have stood beside Dugdale, and thanked her for "reminding people what Scottish Labour is all about".More news: The Victoria's Secret Fashion Show Is Headed To China!
More news: Despite Trump's claims, very few countries see 7 percent GDP growth
More news: NJ representatives won't hold grudge against Texas, promise to support Harvey aid
Neil Findley, an MSP for the Lothian region, stood against Jim Murphy for the leadership in 2014, after his preferred option at the time, Gordon Brown, ruled himself out of the running.
Who could replace her?
"On behalf of the party, I wish her well". His background may have seemed incongruous to traditional Scottish Labour supporters, but his cheerful and effective efficiency helped her score notable hits against Nicola Sturgeon.
Richard Leonard, a former GMB trade union organiser who was elected to Holyrood in 2016, and Anas Sarwar, Labour's Scottish health spokesman, are now thought to be the most likely candidates to take on the job.
While romance across the political divide clearly suited the two MSPs and should be something to celebrate in an era of political tribalism, in some recesses of the Labour Party a less than enlightened attitude prevails and there are those who have privately questioned the wisdom of the relationship.
The Executive Committee of the Scottish Labour Party will meet next weekend, Saturday 9 September 2017, to agree the timetable and process for a leadership election.
Still with the personal, a long-term relationship ended late previous year (although she has since found a new partner) - and she lost her close friend Gordon Aikman to Motor Neurone Disease. But then again, she leaves with her party in third place at Holyrood.
Nevertheless, she has made a more than decent fist of making the best of a bad job.
Sarwar is the current Ladbrokes favourite to become the next Scottish Labour leader, with the betting firm giving him odds of 2/1. Alex Rowley, Ms Dugdale's deputy, has accepted the role of interim leader.