The TV trade body's report showed that advertisers spent a total of £5.27 billion on spots, sponsorships and product placement on TV in 2015, a 7.4 per cent increase from 2014.
It is the sixth consecutive year of growth for the sector. This has been driven in part by online firms, which are now the second-biggest spenders for TV, according to data from Nielsen.
Companies like Google, Facebook and Netflix invested 60 per cent of their marketing budget on TV in 2015. This added up to £500 million, a 14 per cent increase from 2014.
Facebook was TV's biggest new advertiser, with an investment of £10.8 million. It was followed by gaming company Machine Zone, which spent £6.6 million, and online estate agent Agents Mutual Ltd, which spent £5.9 million.
There were 877 new advertisers last year, including Facebook, which accounted for 2.3 per cent of TV adspend. This includes those who had returned to TV after more than five years, Nielsen's data shows.
Meanwhile motor companies increased their year-on-year adspend by 18 per cent, while finance increased by 17 per cent and household FMCG grew by 14 per cent, the report said.
According to Barb, the most-viewed advertiser in 2015 was Procter & Gamble, with 30.5 billion views. Sky had 21.2 billion views, while Unilever and Reckitt Benckiser each had 20.3 billion views.
Lindsey Clay, the chief executive of Thinkbox, said: "Nothing else has TV’s reach, scale and connection with audiences; no other form of advertising is as trusted.
She added: "Online businesses in particular recognise the impact TV advertising has and have significantly increased their investment recently. This is something we expect to continue in 2016."