Each year about 12,000 entrants take part in the Rome Marathon, with the 20th annual event proving as attractive as ever.
And despite rain early on, the Perthshire North MSP recorded a time of 4:46:45.
Speaking on his Twitter feed, the minister said: "Today I ran my first - and probably only - marathon. It was in Rome and was stunning. Loved it."
Mr Swinney is an active fundraiser and often tackles competitive running events to raise money.
Last year, he ran in the Highland Perthshire Half Marathon to raise funds for the MS Society, which supports those with multiple sclerosis. The minister's wife Elizabeth is a known sufferer of the disease.
The Rome Marathon is a popular training event for the world's long-distance runners. The last nine events were won by athletes from Ethiopia or Kenya.