Booth replaces Graham Rowntree, who will be in New Zealand with England's senior squad for Tests against the All Blacks during June.
Booth, 38, is to link up with current Saxons head coach Steve Bates and Simon Hardy, who guided the Saxons to victories over Ireland A and Italy A last month.
Bates said: "I am looking forward to working with Toby - I've heard a lot of good things said about him.
"Simon Hardy knows him well and has nothing but praise for him, and the way the London Irish pack is going, especially in Europe, is a first-class recommendation for his work."
The Saxons head to Canada and the USA in June, where they will defend the trophy won last season through victory over New Zealand Maori at Twickenham.