There'll be two parts to the testimony: the first on Tuesday before the Senate Judiciary and Senate Commerce, Science, and Transportation committees. It will start at 2:15pm ET on and will stream here. The second will be on Wednesday with the House Energy and Commerce Committee. It will start at 10am ET on Wednesday and will stream here.
Congress has already released Zuckerberg's testimony, so check that out if you think you'll miss the first bit of the broadcast. After the testimony, there'll be questions so make sure you tune in for that even if you've read the statement. If you like billionaires acting apologetic, this is going to be the testimony for you, with lines like: "It was my mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens."