How can I get from Seattle to Victoria, then Victoria to the San Juan Islands and back to Seattle from the San Juan Islands without a car? Do the ferries leave from downtown Seattle? We are traveling the end of July.

http://www.clippervacations.com/dest.../sanjuans.html
http://www.kenmoreair.com/

first of all the only ferry leaving Seattle for Victoria is specific one --leaves daily from next to Edgewater Inn on wharf ..comes back same day. However,that would not much leave time in Victoria...Most people stay over night (or 2-3)
San Juan Jslands "touring" -Ferry leaves from Swartz Bay which is north of Victoria (must be shutle or bus transport available) goes thru Islands and ends up at Anacortes, which is a long way south to Seattle..
Ihave heard there is shutle service to Anacortes available by reservation from Sea-Tac airport.
IMO it is best to book all this through a company like "Gardyloo" noted..
After all this advice--It may be that July and August are booked up !!!!They are the peak months in the
Northwest....

Seattle to Victoria and back on the Victoria Clipper is an easy round trip.

Float planes from Seattle to the San Juan islands is the easiest.

I think trying to do all 3 places on a loop, without a car, is not going to be very practical.

There's a company called Victoria Express that offers once a day passenger only ferry service from Victora to Friday Harbor on San Juan Island that definitely makes your trip possible: Clipper from Seattle to Victoria; Victoria Express from there to Friday Harbor; Clipper from Friday Harbor back to Seattle.

I'm assuming you're not trying to do it in one day however.