The UK's biggest broadcaster blamed economic uncertainty for the 3% drop in ad revenue to £1.67bn over 2016 and is forecasting a 6% drop for the first four months of this year.
Ad revenue growth at ITV had been unbroken since the financial crisis sent it down by 9% to £1.29bn in 2009 (although its ad revenue was flat in 2012).
However, ITV said it outperformed the wider advertising market last year and expected to do so again this year.
Client sectors that decreased their spend included supermarkets, banking, retail, finance and food, though entertainment and leisure, cars, cosmetics and household goods continued to spend.
With ITV’s production business continuing to gain in strength, overall revenues rose by 3% to £3.06bn.
The company disclosed that increased demand for advertising online had helped its online, pay and interactive revenues climb 23% to £231m. Audience consumption of video on demand rose by 42%.
Adam Crozier, ITV chief executive, said: "ITV delivered a good performance in 2016 as we continue our strategy of rebalancing and strengthening the business creatively, commercially and financially.
"The continued growth in revenue and adjusted profit, despite a 3% decline in spot advertising revenues resulting from wider political and economic uncertainty, is clear evidence that our strategy is working and remains the right one for ITV."