I'm a civil engineer but i wanted to write my gate exam in architecture and planning. Am I eligible for that

You shall be eligible for M. Arch courses via gATe exam as studenst with minimum 50% marks in B. Arch or Btech or BE  are eligible for Architecture masters courses via GATE into IITs.
https://engineering.careers360.com/articles/gate-syllabus-for-architecture-and-planning
All details regarding GATe shared above.

Hi,

Yes, you will be able to write the GATE exam in Architecture and Planning as long as you have completed 4 years of Bachelor's course in Engineering/Technology. However, this is not very much advised since the syllabus of Architecture and Planning will be completely different. Also, all undergraduate architects are registered under the Council of Architecture, so you will be missing out on that too. Instead of Architecture and Planning, you can opt for other subjects which have shades of Architecture such as Structural Engineering and more. Hope this helps you.