Using ITA for short flights

Are you going there directly after arriving from a transoceanic flight?
The fastest and likely cheapest way to go from Rome to Venice is by train. 4 hours city center to grand canal. You can’t make it that fast by plane, after considering the air travel check-in and security procedures. In addition neither Rome airport nor Venice airport are near the city center, therefore from Rome to Venice by air you need at least 5 to 6 hours when everything is said and done.
Two train company to consider. The first is the State owned company, the latter a private company that operates only high speed trains. Prices and quality of services are comparable but check both.
www.trenitalia.com
www.italotreno.it

Agree, the easiest way to solve your problem is probably to book a train ticket instead.

If you are already in Rome, then the train is easiest.

If at the airport, take the Leonardo Expres to Termini station and then switch to a train to Venice.

Venezia Santa Lucia is the actual Venice train station.

And... the train offers scenery. The plane doesn't.

Ditto, ditto, ditto to all of the above: take the train!!!!
Get on in the middle of Rome; get out on the island of Venice.
No need for transport to airports located some distance away from the historic centers.
No lengthy security processes; almost no luggage restrictions.
IMHO, a 2nd-class seat on an Italian "fast" train beats the same on a plane ANY day for comfort.

Bring snacks, good sammies, wine, etc. for a (tidy, respectful) on-board picnic. Buy supplies at Roma Termini station before you depart including an opener, if your bottle isn't a twist-off, and a couple of glasses.

Sit back and enjoy the ride!

Buy your ticket after you arrive at the airport. After arrival at FCO we went to the Trentila office and purchased our tickets. Very smooth and easy.

Thank-you very much, everyone!