The SNP's Westminster leader issued an apology after he suggested Ollie Taylor may have broken Covid travel rules.
The politician claimed on the social media site that Mr Taylor lived in the south of England, and questioned why he had taken a photograph of the Northern Lights in Caithness. But Mr Taylor said he had moved to Caithness.
Mr Blackford’s tweet was branded “disgraceful” by Liberal Democrat MSP Alex Cole Hamilton at Holyrood on Tuesday.
"Does she support vigilante action from her MPs like this?” Mr Cole Hamilton asked.
The First Minister questioned whether the issue would be among the main priorities for Scots listening into the session.
But she said: "I also saw that Ian Blackford apologised for doing something that he recognised that he shouldn’t have done on Twitter.
"I think that’s the right thing when people get something wrong is to apologise for it and I think that’s the grace and dignity I associate with Ian Blackford every single day of the week.”
Mr Blackford has now deleted the initial tweet.
"As the local MP for Ross, Skye and Lochaber I know my constituents feel very strongly about the breaking of travel restrictions that we see across the Highlands and islands, which puts people's lives and our public services at risk,” he posted.
"I will continue to stand up for my constituents who frequently raise these concerns with me, but I recognise that it was wrong to query an individual on Twitter and I apologise to @OllieTPhoto for my earlier post, which I have deleted."
Tory MSP Annie Wells responded to Ms Sturgeon’s defence by saying: “It was pretty cowardly that the First Minister didn’t do the right thing this afternoon and call out the SNP’s Westminster leader for harassing a private citizen.
“Ian Blackford should be ashamed of himself. He purposely went after an individual who simply wanted to share a lovely photo on Twitter for people to enjoy.
“I’m afraid it is the same old story with the SNP – stoke up division, and when challenged, simply hold up their hands feigning innocence. It is pathetic."