Kightly, 31, previously represented Southend between 2003 and 2005, making 19 appearances for the Essex club before joining Grays Athletic.
The attacker made nine appearances for Burnley last season, but spent the second half of the campaign on loan at Burton Albion, where he scored four times in 12 Championship appearances.
Southend boss Phil Brown told the club's official website: "I think it's a massive signing. As far as I'm concerned, the more quality and ex-Premier League-experienced players we can bring to the football club, it emphasises one the statement of intent from us and two where we want to go.
"The players that I'm bringing in know what it's like to play at a higher level and if they can drag every ounce of effort and quality from the players that we've already got at the football club to try and get us there, then it's job done."
Kightly has also previously represented Wolverhampton Wanderers, Watford and Stoke City.