Weis obtained her B.Sc in Geology and Mineralogy (1979) and PhD (1982) from the Université Libre de Bruxelles (Belgium). She later completed a master's degree in Environmental Sciences (1983) and Habilitation Geochemistry (1992) at Université Libre de Bruxelles.

She later undertook Postdoctoral Research Fellowships at University of Paris VII (1984) and California Institute of Technology (1985–7). Weis was also a Chercheur Qualifié FNRS (1985–1993), Maître de Recherches (1993–1998) and Directeur de Recherches (1998–2001) at the University of Brussels, Belgium.

In 2002, Weis was appointed a Tier 1 Canada Research Chair at the University of British Columbia in Vancouver, Canada as she established the Pacific Centre for Isotopic and Geochemical Research (PCIGR).^[1] In this role, she published "High‐precision isotopic characterization of USGS reference materials by TIMS and MC‐ICP‐MS" in the journal Geochemistry, Geophysics, Geosystems.

By 2009, she was the recipient of the Killam Faculty Research Senior Fellows Award^[2] and renewed as a Canada Research Chair.^[3] The following year, the PCIGR was approved for funding from the Canada Foundation for Innovation and B.C. Knowledge Development Fund. This allowed the centre to update its geochemical analytical equipment.^[4] As a result of her research, Weis was elected a Geochemical Fellow by the Geochemical Society and the European Association of Geochemistry.^[5]

In 2016, Weis was elected to sit on the Geochemical Society Board^[6] and a Fellow of the Royal Society of Canada.^[7] In the following years, she was also renewed as a Canada Research Chair in the Geochemistry of the Earth’s Mantle^[8] and named President-elect of the Volcanology, Geochemistry, and Petrology Section of the American Geophysical Union.^[9]

Weis' innovative use of trace element and isotopic geochemistry spans a wide range of applications in the Earth and environmental sciences. Her research interests include the distribution of elements and isotopes in Earth systems with an emphasis on the use of abundances and isotopic ratios in earth (petrology/volcanology/geochronology) and environmental sciences. This includes defining the source and evolution of igneous and metamorphic rocks, the interactions between different reservoirs (mantle, crust and atmosphere) and the role of tectonic settings. Other interests include geochemical and isotopic studies of sedimentary rocks, global changes and reconstitution of past environments; distribution of pollutants in natural and anthropogenic systems; application of non-traditional heavy stable to environmental issues and analytical technique developments, techniques for high precision chemical and isotope analysis.