Merz and McLellan was a leading British electrical engineering consultancy based in Newcastle.
The firm was founded by Charles Merz and William McLellan in Newcastle upon Tyne in 1902 when McLellan joined Merz's existing firm established in 1899. The partnership was instrumental in designing the United Kingdom's first three-phase electrical supply network, on Tyneside, and for the next century continued to advise other Commonwealth countries on setting up their own networks.
In 1995 the partnership merged with the Parsons Brinckerhoff consultancy, and in 2000 the new owners announced that the Merz & McLellan name would be discontinued.
In 2010, Mott MacDonald consultancy announced  that it had bought Merz and McLellan South Africa.
- 1901: Neptune Bank Power Station
- 1904: Carville Power Station, Wallsend, UK
- 1911: Electrification of North Eastern Railway (UK)
- 1914-18: Mobile power stations for the battlefield
- 1921: North Tees Power Station
- 1925: Electrification of the Lyttelton railway line between Lyttelton and Christchurch, New Zealand
- 1933-51: Dunston B power station, Dunston, Newcastle-Upon-Tyne, UK
- 1940s: Orlando Power Station, Johannesburg, South Africa
- 1953: Blyth A Power Station, Cambois, Northumberland, UK
- 1960s: Bell Bay Power Station, Tasmania, Australia
- 1962: Blyth B Power Station
- 1969 Longannet Power Station
- 1980-1993: Kariba South dam hydroelectric upgrade
- 1989: Subiya oil-fired power station, Kuwait
Merz & McLellan firms still independent