The 26-year-old left-back signed on a free transfer from Hamilton in the summer, also scooped Rovers' goal of the season gong for his winner on his debut at Leyton Orient.
Despite Ronnie Moore replacing Les Parry in the Prenton Park hotseat in March, Buchanan has remained a constant, clocking up 44 appearances in all competitions.
"I want to thank all the fans who voted for me, it means a lot to me," he told Tranmere's official website.
"I couldn't have asked for anything more. I came in at the start of the season and people didn't know too much about me.
"Obviously the fans have taken to me and they've been brilliant all season. Since Ronnie has come in the team have kicked on, we've been hard to beat and it has been great to keep so many clean sheets."