He became astronomy professor at Leiden University in 1988, served as the observatory's scientific director 1996–2003, was appointed to a Royal Netherlands Academy of Arts and Sciences Professorship 2003–2008.

From 1984 to 1988 he was senior astronomer and head of academic affairs at the Space Telescope Science Institute in Baltimore, as well as an adjunct professor at Johns Hopkins University.

Construction for this telescope, which Miley had dubbed LOFAR, for Low-Frequency Array, began in 2006, led by the Netherlands Institute for Radio Astronomy ASTRON.

When the telescope was completed in 2017, it consisted of a phased array of 20,000 single antennae in 48 stations, located in the Netherlands, Germany, France, Poland, Great Britain, and Ireland.

During his term as vice-president of the International Astronomical Union, Miley designed the IAU strategic plan "Astronomy for Development," whose main goal was to exploit astronomy for advancing the United Nations sustainable development goals.The strategic plan was adopted at the IAU General Assembly in Rio de Janeiro in August 2009.