[7][8] She earned a PhD at Princeton University from the department of astrophysical Sciences with advisor David Spergel, where she first worked on the Wilkinson Microwave Anisotropy Probe (WMAP).

In 2009, Peiris won a Leverhulme Trust award for cosmology and secured a faculty position at University College London.

[15] In 2012, the WMAP team (including Peiris) won the Gruber Cosmology Prize for their "exquisite measurements of anisotropies in the relic radiation from the Big Bang—the Cosmic Microwave Background".

[18] Her skepticism proved well-founded: on 30 January 2015, a joint analysis of BICEP2 and Planck data was published and the European Space Agency announced that the signal can be entirely attributed to dust in the Milky Way,[19] though (non-primordial) gravitational waves have since been detected by different experiments.

In 2018, Peiris was awarded the Hoyle Medal and Prize of the UK Institute of Physics for "her leading contributions to understanding the origin and evolution of cosmic structure.

[30] In 2014, the pseudonymously-written Ephraim Hardcastle diary column in the Daily Mail claimed that Peiris (along with Maggie Aderin-Pocock) had been selected to discuss results from the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP-2) experiment on BBC Newsnight because of her gender and ethnicity.

These comments were condemned by mainstream media, the Royal Astronomical Society and Peiris' employer, University College London,[31][32] and the Daily Mail and its column backed down within days.