Additional District and Sessions Judge B K Tyagi held Sumit Kumar and his sister-in-law Aruna guilty under section 302 (murder) of the IPC.
A fine of Rs 12,000 was also imposed on each of them.
Sumit with the help of Aruna shot dead Ashwini Sharma at Bhorakhund village here in April 2014, government lawyer Yashpal said.
The accused were in an illicit relationship and Ashwini had found out about it, the lawyer said.