Gilles Toussaint
Founder at GT Impact
Founder of GT Impact and host of the Mission First podcast: the PhD chemist turned greentech growth marketer with one rule, that in climate tech you cannot have an impact without first making a profit.
Compiled by Antoine Walter - from insight gathered on and off his (don’t) Waste Water microphone!
Gilles Toussaint is the founder of GT Impact, a Berlin growth-marketing consultancy that helps greentech and climate startups turn good technology into real revenue, and the host of the Mission First podcast. A PhD chemist who left the lab for marketing, his message on the show was blunt: in greentech you cannot have an impact without profit (as of 2026).
Gilles Toussaint did not set out to be a marketer. He earned a PhD in chemistry at the University of Liege in Belgium and spent the better part of a decade in research and development, including a stretch at Prayon developing cathode materials for the lithium batteries that go into electric vehicles. Then he walked away from chemistry entirely, moved to Berlin, and rebuilt himself from scratch in the startup world, first co-founding a hardware company he later sold, then teaching himself sales the hard way at ResearchGate, the social network for scientists, where he became one of the top sales performers on the team.
Gilles Toussaint founded GT Impact in 2019 to solve a problem he kept seeing up close: greentech and climate companies that have genuinely good technology and almost no idea how to sell it. He works as a fractional CMO, which is a chief marketing officer you hire part-time and embed in the team rather than on retainer for a slide deck, running growth for sustainability-minded startups like Tracklib, Planet Wild and iMusician. The companies he likes are usually in the deep-tech or greentech space, the kind of water and climate builders whose product is real but whose market still has to be taught why it matters.
Gilles Toussaint's central argument is one a lot of mission-driven founders find uncomfortable, which is that you cannot have an impact without making a profit, because profit is really a measure of how much of your customer's problem you actually solved. His second rule follows from the first: talk to your market from the very beginning, before the product is even built, the way the best founders already do when they start telling their story on LinkedIn and at trade fairs from day one. The founders who get that, he argues, grow far faster than the ones who treat marketing as something you bolt on later.
Gilles Toussaint built the Mission First podcast, full name Mission First - Entrepreneurs for Future, on that same conviction, interviewing founders whose companies are tied to a real mission and pulling out the concrete dos and don'ts of growing a young company. More recently he has moved from selling the growth playbook to building with it, co-founding Life on Marsh, a venture making wetland restoration measurable and financeable as a climate asset, which quietly brings the former battery chemist back toward water. There is also a second thread running underneath all of this, because the same person who left chemistry for startups also left it for music, founding the biggest music-industry meetup in Berlin and playing in a band, which is a useful reminder that the growth playbook he sells is one he first learned building an audience for himself.
“I really believe that you should discuss with your market and you should discuss with a potential audience from the very, very beginning.”
Gilles Toussaint is, in the end, a translator: a scientist who can speak the language of founders building hard climate technology and the language of the customers who have to be convinced to buy it, which in greentech is most of the gap between a good idea and a real company.
On (don’t) Waste Water
Gilles Toussaint joined (don’t) Waste Water once, for a deep dive on growth marketing for greentech companies:
The company
Frequently asked
- Who is Gilles Toussaint?
- Gilles Toussaint is the founder of GT Impact, a Berlin-based growth-marketing consultancy for greentech and climate startups, and the host of the Mission First - Entrepreneurs for Future podcast. A PhD chemist who left research for sales and marketing, he works as a fractional CMO helping mission-driven companies turn technology into revenue.
- What is GT Impact, and what does Gilles Toussaint do?
- GT Impact is Gilles Toussaint's growth-marketing consultancy, founded in 2019 in Berlin. Toussaint works as a fractional CMO, embedded part-time in a startup's team, building the marketing, sales and growth engine for greentech, climate-tech and SaaS companies so they can acquire customers and grow revenue, not just ship good technology.
- What is the Mission First podcast?
- Mission First - Entrepreneurs for Future is the podcast Gilles Toussaint founded and hosted from 2020 to 2024. Each episode interviews a founder whose company is tied to a real mission, from greentech to ocean conservation, pulling out concrete lessons on growth, funding and business models. It was named a top sustainability podcast in 2020.
- How did Gilles Toussaint go from chemistry to marketing?
- Gilles Toussaint earned a PhD in chemistry at the University of Liege and spent years in R&D, including developing lithium-battery cathode materials at Prayon. He then left chemistry, moved to Berlin, co-founded and sold a hardware startup, and taught himself sales at ResearchGate before becoming a marketing chief and founding GT Impact.
- Where is Gilles Toussaint based, and where can I hear his episode?
- Gilles Toussaint is based in Berlin, Germany, where he runs GT Impact. He appeared on the (don’t) Waste Water podcast in 2021, in an episode on growth marketing for greentech companies, arguing you cannot have an impact without profit. That episode is linked above to read, listen or watch.
- Is this the same Gilles Toussaint who works in water?
- Gilles Toussaint here is the growth marketer and founder of GT Impact, not to be confused with namesakes in journalism or other fields. His link to water is recent and indirect: he is co-founding Life on Marsh, a venture making wetland restoration measurable and financeable, which brings the former battery chemist back toward water resilience.