Mr Galan will join the Prime Minister in Scotland on Friday as Sir Keir convenes the UK’s first Council of Nations and Regions.
ScottishPower owns the distribution network for central and southern Scotland, Merseyside, North Wales and parts of Cheshire and Shropshire, supplying energy to 4.4m homes and businesses.
It also owns the high-voltage national grid network for southern Scotland and is one of the UK’s biggest onshore wind developers, owning 38 onshore wind farms with 1,157 turbines.
Friday’s announcement makes the UK the largest investment destination for Iberdrola, which also has significant holdings in Spain, America, Brazil and Mexico.
About two-thirds of the money will go towards improving the size and scope of the grid, which is expected to come under strain because of the shift to renewables.
That will include building a new so-called electricity superhighway, Eastern Green Link 1, between Torness in southeast Scotland and Hawthorn Pit in County Durham.
Iberdrola’s August £2.1bn buyout of Electricity North West, which runs the grid across much of North West England, is included in the £24bn figure.