This study contributes to our knowledge on the association between parenthood and psychological well-being by examining whether pre-parenthood lifestyles (leisure and paid work) moderate the transition to parenthood. We expected that people with less active lifestyles would find it easier to adapt to the demands of parenthood. Using eleven waves of the Swiss Household Panel (N = 1332 men and 1272 women; 1999–2008, 2010), fixed effects models are estimated for men and women separately. Results show that—on average—parenthood was not associated with well-being for men, whereas it increased wellbeing for women. As expected, the well-being premium/cost to parenthood was contingent upon individuals’ lifestyle before the transition to parenthood. For men, parenthood reduced well-being, but only if they frequently participated in leisure before the birth of the child. For women, motherhood had a beneficial effect on well-being but this effect was weaker for women who combined leisure with working long hours before motherhood.