The Foster City, California-based firm's leading hepatitis C treatments, Harvoni and Sovaldi, brought in $3.6 billion and $1.3 billion in quarterly worldwide sales, respectively.
Analysts had expected revenues of about $3.47 billion for Harvoni and $928 million for Sovaldi, according to StreetAccount.
Gilead now boasts a market share of more than 90 percent of all hepatitis C patients, Paul Carter, Gilead's executive vice president of commercial operations, said on the earnings call. He added that this market is still in its early days.
"We see encouraging trends, and remain highly confident," he said of the U.S. market for its hepatitis C treatments, later adding that the company also predicts a strong future in Europe.
HIV treatment Truvada, meanwhile, saw its sales rise 5 percent over the same period last year to $849 million—besting an average analyst expectation of $795.8 million.
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The company also said Tuesday that it was projecting full-year net product sales between $29 billion and $30 billion. That surpassed April's full-year guidance of $28 billion to $29 billion.
Sanford Bernstein analyst Geoffrey Porges called the results "spectacular," adding that the higher 2015 sales forecast "suggests that there's substantial EPS upside versus current consensus," Reuters reported.
On the company's earnings call, Porges said this quarter's guidance was "probably the most remarkable" he's seen in some time.
Gilead Sciences is aggressively looking to expand the presence of its new treatments for hepatitis C and human immunodeficiency virus, as well as its pipeline, in order to offset upcoming patent expires for many of its mature products, according to research firm Piper Jaffray, which has an "overweight" rating on the stock.
Harvoni and Sovaldi accounted for $4.55 billion, or 60 percent, of Gilead's revenue from January to March.
Gilead trades at a discount to other large-cap biotech stocks, with a 2016 price-to-earnings ratio of about 11, the lowest in its class, Piper Jaffray said in a note on Friday.
As of Tuesday afternoon, Gilead shares had gained about 23 percent over the last year, underperforming the S&P 500 biotechnology subsector, which increased about 30 percent over the same period.
—CNBC's Karma Allen and Reuters contributed to this report.