Merchant and land speculator, Waldo hailed from Massachusetts. His land speculations were in the areas of the Penobscot and Muscongus Rivers (present-day Maine); where, on his own account, he brought in and settled a number of German families. In 1730, he bought from an English gentleman, rights to lands which he claimed were rooted in the royal patent which, 1621, had been granted to Sir William Alexander. (Over the whole of his life, Waldo asserted his ownership rights to a massive area which included parts of Nova Scotia, indeed, he pleaded his case in London. He never succeeded in getting anyone to recognize these rights.)
Waldo was a good friend of both Pepperrell and Shirley; though with Shirley, in later years (1749), he had a falling out over military accounts.
Waldo numbered among those merchants in New England who were anxious to get rid of their French rivals once and for all; besides, to Waldo, getting rid of the French would help him with his various land claims. In 1740, Waldo enthusiastically produced a military plan which included the taking of Louisbourg. In the winter of 1744/45 we would have found Waldo, together with Shirley and others pouring other military plans in their candle lit dens at Boston.
Thus, Brigadier Waldo's main claim to fame was that he was part of the New England forces of 1745 which took Fortress Louisbourg. It had been intended that he should be second in command to Pepperrell; but, he was trumped by Roger Wolcott, the 67 year old deputy governor of Connecticut (it seems it was a condition for Connecticut's involvement). Waldo had to be satisfied in heading up his own Regiment, "The Second Massachusetts" which was actively commanded by Colonel Arthur Noble.
Likewise, Waldo became involved in the taking of Louisbourg in 1758. He submitted a detailed plan of attack to William Pitt, a plan which Pitt used as the basis for his instructions to Major Jeffrey Amherst.
[See DCB; and, in reference to Waldo's plans, see the citation of the letter (Waldo to Pitt, Nov. 7, 1757) P.A.C., C.O. 5, vol. 52, as cited by Hitsman and Bond (Hitsman, C.H.R., at Fn p. 320).]