The tax on sugary drinks drove their sugar content down 29 percent, Public Health England figures show.
However, efforts to persuade manufacturers to voluntarily cut sugar in their food by one-fifth by next year are off target.
The amount of sugar in the food we buy in stores actually increased over the same period from 2015 to 2018.
Experts said parts of the food industry were "asleep at the wheel," but chiefs said the government's goals were ambitious.
Obesity increases the risk of type 2 diabetes and heart disease and is putting millions of people at risk for cancer.
But Prime Minister Boris Johnson openly questioned whether "sin taxes" really reduce obesity.
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Did the sugar tax work?
The sugar tax – officially the soft drink industry rate – was introduced in April 2018.
It charges manufacturers 24p per liter for very sweet drinks and 18p per liter for medium sugar drinks.
Brands like Fanta, Ribena and Irn Bru changed their recipes in response.
On average, 100 ml of sugary drinks now contain 28.8% less sugar than in 2015.
Soft drink sales increased between 2015 and 2018, but moved to low or zero sugar versions.
This results in more than 30,000 tons less sugar – 5 billion fewer calories – being sold in such drinks each year.
What about everything we eat?
Progress in pop sugar content contrasts sharply with that of other foods.
Public Health England has a voluntary sugar reduction program with food manufacturers and retailers.
Children's favorites – including cakes, chocolate, breakfast cereals, yogurts and cookies – are being targeted.
The goal is to reduce the average sugar content by 20% by 2020 compared with 2015 levels.
By 2017, the value cut had reached 2% and by 2018 (the latest data we have), the number had risen to 2.9%.
There should have been a 5% reduction in the first year of the plan.
Sue Kellie of the British Dietetic Association said it was a "worrying lack of progress" and "very unlikely" that the goal would be reached.
So are we eating less sugar?
Apparently not, at least when we're home.
Despite the success of the sugar tax and the 2.9% cut in sugar due to food reformulation – we are still eating more.
The report says that the amount of sugar in grocery-bought foods has increased from 723,000 tonnes in 2015 to 743,000 tonnes in 2018.
PHE officials said this is equivalent to everyone increasing their sugar consumption by 0.5%.
This may be because we are buying more or larger portions.
There was also a large increase in ice cream and ice cream sales in 2018, possibly due to the hot weather.
What was the reaction?
Duncan Selbie, chief executive of Public Health England, said there was "some encouraging progress" from the food industry that he described as "realistic at this early stage".
Russell Viner, president of the Royal College of Pediatrics and Child Health, said the sugar tax is a "success story." But he said the food industry in general "is deeply asleep at the wheel – it's time for a warning."
He added: "If the industry does not act on child health, we expect the introduction of mandatory sugar reduction targets by 2020."
The Food and Beverage Federation said the industry is committed to cutting sugar.
But he added: "England's Public Health has set immensely ambitious goals and could never be achieved in all categories within the ambitious time frame."
Could the sugar tax be extended?
There are no current plans. However, the idea was raised.
The leading doctor of England, Profa. Sally Davies had already accused the food industry of "failing the public".
In May this year she said, "I want parents to be encouraged to buy healthy foods.
"We need to ensure that fresh fruits and vegetables are cheap.
"We may have to subsidize them by charging more, taxing unhealthy foods."
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