Rob Lawrie, 49, from Leeds, admitted to a court in Boulogne that he tried to get Bahar - known as Bru - into the UK.
He faced smuggling charges but was found guilty of a lesser charge of 'endangering life' because he hid the girl in an unsafe way in a van.
Lawrie will have to pay the 1,000-euro (Â£754) fine if convicted of another offence.
The decision was met with applause from supporters in the courtroom.
The former carpet cleaner, who disclosed he had bipolar disorder and Tourette's Syndrome, said he acted "stupidly".
Before the case started he appeared with the child on his lap at a media conference in the French town.
Lawrie said he feared "being made an example of" by the court.
He told the assembled media: "They see the media attention I have been getting and I think it could go one of two ways.
"France has an opportunity to show, as I know they are, a compassionate country."
Lawrie said he regretted his actions and would not repeat the effort.
He told the court he had acted stupidly and irrationally in hiding Bru in the sleeping compartment.
Speaking via an interpreter, he told the judge: "I saw the little girl and her father in the work that I was doing. That night I just could not leave her there any more.
"It was wrong. It was the most stupid conceived plan."
Lawrie rejected the idea that he was trafficking for money, telling the judge: "Her father is a farmer from Afghanistan. He doesn't have any money whatsoever."
The aid worker was stopped in Calais as he returned home in October 2015.
The former Army physical training instructor said he was helping build shelters in The Jungle camp when he got to know Bru and her father asked him to help get her to close family members living legally in Leeds.
He said he was not a hero but "an unemployed carpet cleaner from Leeds" who wanted to help and had never been in trouble before.
He told reporters his actions had left him penniless and on the edge of bankruptcy after giving up to Â£8,000 of his own money as well as collecting donations for the refugees.
He was caught when British sniffer dogs found two Eritrean men who, unbeknown to him, had also stowed in the back of his van.
Speaking outside the courtroom, Lawrie said that he had had a heavy weight on his shoulders but now felt "light" and would continue fighting to get help for child refugees in The Jungle.
He said: "I'm going to have a few days off and then I'm going to raise the profile (of refugees) even more because we cannot simply leave these children.
"We need to get these children now and into our education system because these guys are going to be doctors and lawyers and teachers if we get them now and educate them correctly.
"Or we can leave them in The Jungle to rot and die of cold."

Airbus increased revenue by 6% in the third quarter to €14bn (£10bn; $15.4bn) compared with €13.3bn the year before.
The company benefited from the strong dollar and growing sales across all its products.
Airbus plans to increase production of its A320 to 60 a month in 2019, from 42 now, capitalising on growing sales.
Shares in Airbus rose 4.6% in early trading following the news.
The company's order intake increased 42% in the first nine months of 2015 compared with a year earlier. Airbus did €100bn in sales of commercial aircraft and  €4bn of helicopters sales.
The firm also announced a €1bn share buy back to be completed by mid-2016.
Airbus said the increased production of A320s would help off set some of the issues it has had delivering other aircraft.
In a statement, chief executive Tom Enders said "We are strongly focused on programme execution given our key operational challenges with the A350 and A400M ram-ups."
Airbus has struggled to keep up with demand for its A350. Both the A350, and the  A400M military aircraft, have carbon fibre structures that improve fuel efficiency.
A former soldier caught trying to bring a child into the UK has been given a suspended fine by a French court.
[NEXT_CONCEPT]
European aircraft maker Airbus is planning to ramp up production of its A320 following a profitable third quarter earnings.