After four years, in 1723, he returned to Paris and was elected top the Paris Academy of Sciences as an adjoint for Geometry. In 1724 he published a treatise of the mathematics of musical instruments.
In 1728 he travelled to London and was made a member of the Royal Academy, and in 1729, travelled to Basel to study mechanics and differential calculus with Johann Bernoulli (I).
In the early 1730s, Maupertuis got interested in the exact figure of planet Earth, i.e. the deviation from the spherical shape, as well as the figures of celestial bodies. Following Newtonian mechanics, he thought these bodies should be of ellipsoidal shape. In his treatise of the figures of the celestial bodies (Maupertuis 1734), he included a translation to French of Derham's catalog of "Nebulae."
In 1735, the Paris Academy sent two expeditions for investigating this thread, the first, under the direction of Charles-Marie de la Condamine, went to Peru and Ecuador, the second one, commanded by Maupertuis, to Lapland. Surveying work was done in 1736; despite considerable errors, the results demonstrated the oblateness of Earth's shape.
In 1741, he became Vice President of the Paris Academy, and little later was made this academy's President. But academic dispute and quarrel ended in his soon dismission. In 1745, he went to Berlin to become director of the Royal Academy there. Again, he got involved in academic trouble; this trouble together with increasing health problems caused him to leave.
He returned to France, but soon travelled to Basel where he stayed until his death on July 27, 1759 in the house of Johann Bernoulli (II).