The Maternal Employment and Happiness study by the German Institute for Economic Research (DIW) was based on interviews with around 20,000 women with children under 14 from a range of social classes and professional backgrounds.
It showed that women with full-time jobs in Europe's biggest economy reported the highest levels of life satisfaction.
DIW said 39 percent of mothers with children under 14 do not work outside the home, although 58 percent of those women said they would like to.
Nearly one in five, or 18 percent, of women with children younger than 14 works full-time.
The researchers said the extent to which women felt they had a say in whether or not they were working had a strong impact on their happiness.
"The negative effect of not working or working part-time on the life satisfaction of mothers is not as grave as when they are unemployed but it is still apparent," the study's author, Eva Berger, said.