Flight Crew Air Transport Pilot (ATP)
Time Pressure; Troubleshooting; Communication Breakdown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Took Evasive Action; General Declared Emergency
Procedure; Weather
We where at 15;000 FT into the decent for ZZZ1 when we had large thunderstorms to the left and to the right of the aircraft.  We started to paint a large thunderstorm on our radar in front of us.  We could not see what was behind this thunderstorm in front of us. I then told my First Officer to tell ZZZ Approach Control on frequency 120.5 that we need to deviate to the left for weather.  So my First Officer told the Controller that we need to deviate to the left and the Controller told us unable.  So I told my First Officer to ask him if we can deviate to the right then.  The ZZZ Controller said unable and that he needs us to remain on course.  So at this point I got on the radio and told the Controller that we either have to deviate to the left or right to get around weather and if we cannot do that then we will have to declare an emergency.  The Controller came back and said; 'Then declare an emergency.' So I said; 'We are declaring an emergency at this time for weather.'At that point the Controller let us deviate to the left for about 15 to 20 miles to get around this thunderstorm. We ended up having to go-around several more thunderstorms that where behind this first one and we landed in ZZZ1 safely.I believe that these controllers need to understand that we cannot fly through thunderstorms under any circumstances and that when we need to deviate for weather; we need to deviate.  They need to work the traffic more around the aircraft that has to deviate for weather and not tell that crew that has to deviate that they are unable and that they need to remain on course.  That's how aircraft go down is when they fly into severe thunderstorms and not being able to see on radar what is behind the first thunderstorm.  As pilots we need to remember that ATC provides us a service and to not let ATC fly your aircraft for you.  That you and your crew need to take control and fly your aircraft and if you have to declare an emergency for weather or any reason in the interest of safety then do it.  Do not hesitate you have many lives in your hands and everyone is counting on you to get them to their destination safely.
Pilot describes situation where they need to deviate around weather and Controller denies the request until pilot declares weather emergency.