Aedas derives from the Latin word aedificio, meaning "to build".
The alliance will have more than 800 staff working from 14 offices in six countries, with 450 employees in the UK. Its turnover will be £30m.
The alliance's board will have five directors, including James Handley and Peter Oborn from Abbey Holford Rowe, two directors from LPT and one from Peddle Thorp.
Oborn told staff in the London office about the move on Friday last week. The firm's clients were sent letters confirming the details early this week.
LPT approached Abbey Holford Rowe 18 months ago for help in education design, an area in which the UK practice specialises. LPT believed then that education was about to boom in Hong Kong. The expected boom did not occur but the firms were ambitious to develop a global brand. Peddle Thorp already had a relationship with LPT.
Oborn said: "We were considering changing our name anyway, as we thought it was time to refresh our image."
The company's new name will be introduced on 1 June.