The man, only known as Paul, went down on one knee to propose to Ian during a public meeting in Oban, Argyll on Monday night.
But he decided to enlist the help of the visiting First Minister, who put forward the marriage proposal on his behalf.
The proposal was captured on camera, and Sturgeon shared the picture on Twitter saying it was her “favourite” moment from the meeting.
The snap shows Paul down on one knee, smiling as Sturgeon has an arm around his shoulders.
With her other arm she points at Paul and asks a grinning Ian to marry him.
She captioned the photo: “Fave moment of Oban public meeting tonight captured in this pic.
“Paul (seen here on one knee) asked me to deliver his marriage proposal to Ian on his behalf.
“I’m delighted to report that Ian said yes. Congratulations to them both.”
Her fans dubbed the moment “amazing” and said they had “never been prouder to be Scottish”.
One follower, Jay, said: “This is amazing. You must be the first head of any government to do this?”
Another wrote: “I have never been more proud to be Scottish. Talk about leading by example.”
Iain Beale joked: “I wish the 55% would’ve listened to you like Ian did.”
Kaiser Desmond also made reference to the referendum, tweeting: “You mean they thought they were better together?”
The public meeting was held in Oban’s Atlantis Leisure Centre, where the public were able to chat face-to-face with politicians.
The First Minister attended with her Cabinet, following successful visits earlier this year to Ullapool, Dumfries and Aberdeen.