Speaking with CNBC's "Squawk Box," Mellon said the days of rapid growth for the companies are behind them as increased government regulation looks more likely.
"These fatted calves are now ripe for the plucking by governments everywhere," he said, adding that tech companies were going to be "pillaged" by administrations across the world.
Drawing a comparison to the increased scrutiny faced by banks following the 2008 global financial crisis, Burnbrae Group's Mellon said the fines are going to be "enormous" and will likely be "bigger than those being levied on the banks in the last decade or so."
Turning his attention to Facebook, Mellon said: "If I was Mr. Zuckerberg, I'd be looking at a halving of my share price in the next couple of years, basically."
"The Cambridge Analytica thing is just the tip of the iceberg, in my opinion," Mellon said, referring to the ongoing scandal related to the political analytics firm's use of Facebook user data.
"We're going to see decimation of particularly Facebook," he added, saying that it was a "trivial use of modern technology and one that's rather sinister."
Mellon has been historically bearish on big tech stocks and is no stranger to controversy. In 2016, following the U.K.'s historic decision to leave the European Union, he told CNBC that "the euro is gone within three to five years, as it currently exists."
Asked about the areas of tech that investors should look at, Mellon cited biotech as a sector to watch, with its ability to "have a positive impact on human beings as opposed to a time-wasting impact on two billion people around the world."
A known advocate of the industry, Mellon has written books on the how investors can benefit from advancements in the biotech space. Some of the companies that he has said he likes in the area include Gilead, Editas and Adaptimmune.
"There's stuff out there now that's going to keep people alive till a 110 or 120," he said. "This is not science fiction in the future."
As technologies such as gene therapies, stem cell therapies and organ transplants from animals to humans become commonplace, the average human life expectancy could reach 150, Mellon said.
Saying that there were great investment opportunities in the sector, Mellon asked: "If we do live to a 120, how are you going to support yourself? The government's not going to do it."
"You might as well invest in the things that keep people alive longer and in healthy condition."