Mobile payments company Square started trading on the NYSE at $11.20 a share on Thursday. Shares closed at $13.07, up 45 percent from their trading debut.
A day earlier, the company had priced its initial public offering below the range it previously outlined.
Square priced its IPO at $9 per share after the bell Wednesday. Earlier this month, the company set the price range at $11 to $13 a share, valuing Square at up to $4.2 billion, or 30 percent less than in a private fundraising round a year ago.
Shares traded as high as 50 percent in the moments after the stock opened.
"It's all about getting the business and accelerating the business, and that's what we came here to do today and we did it," said CEO and co-founder Jack Dorsey in an exclusive interview on CNBC.
Dorsey is also the CEO of Twitter. He added that the focus will not be on trading Square's stock, but rather on growing the business.
Square's IPO is currently in the top 10 debuts this year of companies valued over $1 billion, even though it priced below its expected range.
"We are entering a new market and we're really excited to get back to work," Dorsey said. "We have a long-term view on our business and where we need to go and what we need to do and we just want to build good tools that people love."
The company is one of the most prominent "unicorns," or private companies valued at $1 billion or more, to plan a public debut this year. Larger shareholders appear to want a discount on the stock for assurances it performs well, and advisers have recommended a lower-than-expected price to the company, sources had told CNBC before the final pricing was announced.
In the nine months ended Sept. 30, Square took in $892.8 million in total net revenue, according to a Securities and Exchange Commission filing. Total net revenue rose 49 percent from the same period in the previous year.
Square posted a net loss of $131.5 million in the nine months ended Sept. 30.
— CNBC's Kayla Tausche and Reuters contributed to this report.