The 23-year-old will become the Citizens' club-record signing once agreeing personal terms, surpassing the fee paid to sign Kevin De Bruyne from Wolfsburg (£55m) when factoring in the fluctuating exchange rate.
Laporte, who is understood to have passed a City medical in Bilbao last week, has wished his club of eight years all the best ahead of travelling to Manchester and finalising a big-money switch on either Monday or Tuesday.
"I have a lot to say in very few lines," he said in a statement. "I want to thank you for all that you have given me I came here as a teenager and here I grew up to be an adult and into a footballer.
"I don't want my departure, before beginning a new challenge in my professional career, to be a goodbye, but rather a see-you-soon. Here I leave a unique club, different and which I will never forget."
Athletic youth product Laporte was due to see his contract at San Mames expire at the end of the 2019-20 season.