Nearly 80 percent of more than 18,000 adults questioned in an online Ipsos poll in 15 countries who were part of a couple said they were happy, compared with 67 percent of singles.
Canadian couples were the most content at 90 percent, compared with 53 percent of Hungarians, according to the survey by the independent market research firm.
"Based on our research, people in relationships say they're happier," said Janis Gilman, global marketing director for Ipsos.
But she added that the survey grouped singles with divorcees and widows, which are "all factors that play a negative role in one's happiness and financial security."
In Japan, 53 percent of singles said they were happy, compared with 77 percent of people in a relationship.
In the United States, 74 percent of singles said they were happy, compared with 89 percent of people in a relationship.
Couples were least happy in Hungary and Spain at around 50 percent. Argentine singles and couples tied, with 65 percent in both groups saying they were happy.
"This could have gone either way, given the trials and tribulations that can come from either circumstance. Being in a relationship could have a lot of positives and negatives," Keren Gottfried, senior research manager at Ipsos, said in an interview.
In addition to happiness, being in a relationship also has a positive impact on financial security, according to the poll.
Swedes reported the highest level of financial security of any country and the greatest gap between singles and couples. Sixty percent of couples felt their financial situation was strong, 20 percent more than singles.
Canada and the United States followed with the next highest percentages of both singles and couples saying they thought their finances were strong.
In the United States, 42 percent of couples said they felt financially secure, compared with 27 percent of single people.
Japan and South Korea tied for the lowest sense of financial security for singles, with only 11 percent.
In Italy and Hungary, more singles than couples reported their financial situation was strong.
Ipsos conducted the online poll between Dec. 4 and Dec. 18, questioning 500 or 1,000 people, depending on the country. The credibility interval is +/- 3.5 percentage points for a survey of 1,000 and +/- 5.0 percentage points for a poll of 500 people.
