I would be boarding a flight from Mumbai to Toronto via London and Dublin (2 Layovers). At Dublin I would require changing terminals from T1 to T2. If my entire journey is booked on a single PNR and I would not have to recheckin luggage, then would I be needing a Transit Visa? (According to the Government of Ireland, I wouldn't, but in anycase, if I would be exiting the terminal or crossing the border in the airport, I might, nevertheless, require some kind of visa). Please help.
Presupposing that you have the required documents to enter Canada, you do not need a visa to connect in Ireland, according to Timatic, the tool used by airlines to check document requirements.
If you need to transfer terminals to catch another flight, there is a clearly signposted walkway from the luggage retrieval hall to Terminal 1. Members of staff at Dublin Airport can point you in the right direction if required.
Walking Between Terminals
A walkway between Dublin Airport’s Terminals 1 and 2 is available for those who have not yet passed through the security checkpoint. However, those landing at Terminal 1 and departing via connecting flight from Terminal 2 do not need to make use of this exit. In this case, the route that you need to take will be signposted, and the cabin crew from your previous flight will help you make the proper connections.