In the final of the 1999 Donegal Senior Football Championship, Devenney broke Martin McHugh's record by scoring 0–14 of his team's 1–19 to their opponents Aodh Ruadh's 1–11. Devenney punctured a lung while playing for his club against Clonoe of Tyrone in the Ulster Championship in 2008. He ignored his injury, sustained in the first half, and carried on until the end of the game—scoring four points and contributing to the decisive goal which won the game for his team—after which he was hospitalised. He also captained his club.
Devenney played Championship football until 2005. He came back in 2007. During this time he played soccer with Portadown.
He often played alongside Adrian Sweeney for Donegal, and played a vital part in Donegal's winning of their first National League title in 2007, passing a late fitness test to play in the final against Mayo.
Devenney was held largely responsible for Donegal winning their 2007 Ulster Championship first round match against Armagh on Sunday 27 May 2007. He scored the vital last-minute goal that saw off the Orchard County by a single point, 1-09 to 1–08, at MacCumhail Park in Ballybofey. However, he never won the Ulster Senior Football Championship during his career. Devenney confirmed his retirement from the top level of Gaelic football on 29 December 2009.
I try not to look back. I try to blank it [the past] out. Because there are too many regrets. It hurts too much. There were good days and good bits, for sure, but the big things like an Ulster and All-Ireland that you were looking for, you never got to and that's why I'm afraid to look back. As I've grown older I'd be wild angry about it. We'd be knocked out of Ulster for playing conventional football, then out of Ulster we could play conventional football as good as anyone. We'd be in the qualifiers and tear through the Longfords and Tipperarys, beat the likes of Meath and Galway. They were the games that sustained you, that's why we played football. But see going up to Clones? I’d be dreading going in the door. There were times I'd be thinking, ‘What am I doing here?’ That was my mindset before a championship match. I didn't want to be there. How the hell was I going to perform? Looking back on it, there was no way it could go right. Because Armagh and Tyrone had us figured out. They’d lock down space. You look at Bernard and Alan Brogan against Dublin in that [All-Ireland] semi-final a couple of years ago. They looked like they wanted to walk off the pitch. Donegal messed with their heads. Bernard was in there on his own. He couldn't make a channel run. When he did get it, right away he was running into three boys. That was me for years.
Devenney currently plays soccer for Gweedore United in the Donegal Junior Football League. He also coaches Naomh Adhamhnáin and does radio commentary for the BBC. He has been critical of the qualifiers the GAA have brought into the All-Ireland Senior Football Championship, saying they have "diluted the Championship season a bit." He has also been involved in a national radio debate hosted by Marian Finucane on the topic of money.
^"Awesome Armagh destroy Donegal". RTÉ Sport (RTÉ). 11 July 2004. Retrieved 11 July 2004. "Brendan Devenney was one of the few positives Donegal would take from the first half. He consistently won his duels with Enda McNulty and the many free kicks he earned suggested that Armagh's blanket defence was not totally impenetrable."
^Duggan, Keith (16 February 2013). "More than a club: the extraordinary dominance of the side from south Armagh". The Irish Times (Irish Times Trust). Retrieved 16 February 2013. "“I have seen them play so much doing radio commentary with the BBC,” says Brendan Devenney. “And being honest, I have become a fan.” Devenney managed his club, St Eunan's, against the Armagh champions in the Ulster club quarter-final last November."