Máire O'Neill

Partner

Máire is a partner in our Corporate Department and Co-lead of the Firm’s Energy, Renewables, Infrastructure and Utilities practice group. She specialises in transactional corporate with a particular emphasis on private equity transactions (acting for both companies and investors) and M&A transactions involving technology, fintech and energy and infrastructure assets.

Máire has vast experience in private M&A transactions as well as advising scaling and established companies and investors on equity investments in the Irish market as well as venture debt providers on the equity aspects of their funding. She also advises on a wide range of general corporate matters, including corporate restructurings (solvent and insolvent) including domestic mergers and capital reductions.

Máire’s recent transactions includes advising:

Sweepr on its sale to Plume
CityJet Holding ApS on its investment in CityJet DAC restructuring resulting in the successful exit of CityJet DAC from examinership
Tines on its $125m Series C equity fundraising (with Unicorn valuation), and on its previous Series B, B2, B3 and Series A and A2 fundraisings
Berkshire Partners’ portfolio company Harvey Performance Company on its acquisition of the ATA Group
The sellers of the Beacon Hospital on its disposal to Macquarie Asset Management
The Irish Times on corporate transactions including the sale of its equity interests in WLR FM, Beat 102-103, Red FM and its acquisition of Score Beo
FinTech Apata.com on its equity fundraisings
Management Team of construction specialists Ardmac on the sale to Purever
Accel on its investments in in Nuitée Travel and Nory
EirGrid plc, the national transmission system operator, in connection with the development and financing of the 700MW HVDC Celtic Interconnector between Ireland and France with a capital cost in excess of €1.6bn and on the national emergency generation projects
Element Investments on the disposal of Terra Solar to Omnes backed Power Capital and Terra Solar II to Orsted
UKG Inc. on its acquisition of the Global Payroll Provider, Immedis Group
Fenergo Group in connection with its acquisition of Sentinels and previously on its acquisition by Astorg and Bridgepoint
Carlyle Cardinal on its sale of The City Bin Company to Thorntons Recycling
DCC plc group on its acquisitions of Naturgy Ireland, Jones Oil, Campus Oil and Iskus health
Supporting our Corporate Restructuring & Insolvency teams advising stakeholders in numerous insolvencies and restructurings

2026 Legal 500 EMEA

"Máire O'Neill is creative, extremely capable, pragmatic and highly reliable in getting transactions over the line and completed on time."

2026 Chambers Global

"Máire O'Neill is able to handle a range of transactions. She is an excellent M&A lawyer who gets deals done and over the line while navigating complicated issues." "She is a bright and knowledgeable lawyer who combines top-notch legal advice with a pragmatic approach." "Máire really understands our business and the types of deals we like to do."

2025 Legal 500 EMEA

"Máire O'Neill goes above and beyond to provide an exceptional service to clients. I have found that Máire has an ability to break down issues and provide succinct advice which you are comfortable relying on." "Máire O'Neill is one of the most diligent lawyers that we work with. She is all over the detail and turns complex work around in a timeframe that would be challenging for virtually all other lawyers."

2025 IFLR 1000

Máire is ranked as a Rising Star Partner in IFLR 1000 for Corporate / M&A.

Practice Areas

Corporate / M&A

Private Equity

Projects

Fintech

Venture Capital & Venture Debt

Related Sectors

Energy & Infrastructure

Technology, Data & Comms

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Article and Insights

19Aug 2026

William Fry Advises Examiner in Harp Renewables and ERJ Capital Examinerships

Our Restructuring & Insolvency team advised the Examiner in the successful rescue and recapitalisation of Harp Renewables and ERJ Capital.

Partner

Barbara Galvin

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Article and Insights

31Jul 2026

Government Fast-Tracks Nine Infrastructure Projects

New Act fast-tracks nine transport, water and energy projects. More designations to follow.

Partner

Máire O’Neill

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News

13Mar 2026

William Fry advises AVK on Europe’s First Data Centre Microgrid

William Fry is pleased to have advised AVK on Europe's first entirely off-grid energy solution for data centres

Partner

Jarleth Heneghan

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Article and Insights

17Feb 2026

Sector Watch: M&A Review 2025

EMU was the largest sector in value terms, with €4.84bn worth of transactions in 2025 – a 25% market share.

Partner

Máire O’Neill

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Article and Insights

11Feb 2026

Irish Business Remains Bullish on M&A Activity at William Fry Event

William Fry launched its 2025 M&A Review with insights from Denis O’Brien and expert panelists.

Partner

Andrew McIntyre

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Press Release

12Jan 2026

William Fry Advises Sweepr Technologies on Sale to Plume

William Fry advises Sweepr Technologies on its recent sale to Plume.

Partner

Máire O’Neill

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Article and Insights

22Dec 2025

Government Approves the Drafting of the Private Wires Bill

Drafting of Private Wires Bill to commence following government approval

Partner

Fergus Devine

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Article and Insights

18Dec 2025

CRU Approves “Historic” Investment Allowance of up to €18.9 Billion for Ireland’s Grid Over Next 5 Years

The Commission for Regulation of Utilities (CRU) has published its Final Determination for Price Review Six (PR6), approving a transformative inves...

Partner

Fergus Devine

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Article and Insights

26Nov 2025

ORESS Tonn Nua Auction Results Announced

The Irish Government has announced the results for the State's second offshore wind auction

Partner

Fergus Devine

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Article and Insights

7Nov 2025

Biomethane Sustainability Charter – a Key Milestone for Renewable Gas

Key Biomethane Strategy Milestone is reached with the publication of the Biomethane Sustainability Charter

Partner

Fergus Devine

Máire O'Neill

Ranking & Recommendations

Practice Areas

Related Sectors

William Fry Advises Examiner in Harp Renewables and ERJ Capital Examinerships

Government Fast-Tracks Nine Infrastructure Projects

William Fry advises AVK on Europe’s First Data Centre Microgrid

Sector Watch: M&A Review 2025

Irish Business Remains Bullish on M&A Activity at William Fry Event

William Fry Advises Sweepr Technologies on Sale to Plume

Government Approves the Drafting of the Private Wires Bill

CRU Approves “Historic” Investment Allowance of up to €18.9 Billion for Ireland’s Grid Over Next 5 Years

ORESS Tonn Nua Auction Results Announced

Biomethane Sustainability Charter – a Key Milestone for Renewable Gas