Auto Trader's revenues rose by 9% to £311.4m and underlying operating profit increased by 19% to £207.2m in the year to the end of March.
Operating profit rose by 18% to £203.1m and profit before tax increased by 23% to £193.4m.
Chief executive Trevor Mather said: "We have delivered another year of strong growth.
"With consumers spending more than double the time researching their next car online than they do offline, we have strived to create greater transparency and therefore trust in our marketplace, benefiting consumers, retailers, and manufacturers alike.
"This in turn continues to increase the value we deliver, making the car buying journey a simpler, more enjoyable and trusted process.
"After a number of years of near uninterrupted growth, and despite the exceptionally high performing first quarter of the calendar year, the industry now expects new car registrations to plateau or decline but continues to anticipate growth in used car transaction volumes.
"The new financial year has started well, and despite the wider political and economic uncertainty, the board is confident of delivering its growth expectations for the coming year.
"We remain focused on enhancing the value of our marketplace and continuously improving the products and services we offer for consumers, retailers and manufacturers."