The survey of more than 350,000 Americans found that wellbeing scores differed according to whether people were married, single, cohabiting, divorced or separated.
Married people had the highest wellbeing score with 68.8 – 2.6 points above the national average. They were followed by single people (65.0), the widowed (63.5), and cohabitees (63.3). Divorcees were found to have a lower wellbeing score (59.7), followed by separated people (55.9).
Wellbeing was measured according to six sub-indexes - life evaluation, emotional health, work environment, physical health, healthy behaviours, and access to basic necessities.
Separated Americans were lowest or joint lowest in each category, but scored especially low on life evaluation, emotional health, and access to basic necessities.
In the life evaluation, they scored 30.7 – 18 points below the national average.
Married people were the only group in the study to score above national average in each of the six sub-categories.
"Notably, they score significantly better than those living with a partner on each, specifically in the areas of access to basic necessities, healthy behaviours, work environment, and emotional health," the report stated.
Single people had higher scores than married people in the areas of life evaluation (53.2 compared to 52) and physical health (79.7 compared to 77.8).
Divorced people were found to have slightly better scores than separated Americans in each of the six wellbeing dimensions.
The report noted: "Separated Americans may have lower scores than divorced Americans, especially on the life evaluation, emotional health, and basic access indexes because the end of their marriages may be more recent than those who are already divorced."
Researchers suggested that the relatively low score for widowed people may be down to age "since older Americans generally have low life evaluation scores and predominantly make up the group of widowed people".
The latest study supports the findings of similar research into wellbeing and marital status carried out by Gallup year on year since 2008.
In the last four years, married people have consistently topped the wellbeing index, while divorced and separated people have consistently scored far lower.
"It is possible that Americans who have higher wellbeing are more likely to choose marriage than those with lower wellbeing, or that some third variable - such as religiosity or age - could be related to both higher wellbeing and one's likelihood of being married," said the report.
"Clearly, marriage has economic benefits and ending a marriage can have serious economic consequences, which helps explain part of the gap in wellbeing by marital status.
"Marriage also brings companionship, emotional support, and partnership in dealing with life's ups and downs that can foster a higher level of personal wellbeing.
"Social interaction is inherently part of marriage, and Gallup analyses have clearly shown that time spent socially and social networks themselves are positively associated with high wellbeing."