Ireland's campaign ended in Windhoek with a five-wicket defeat that handed Namibia a third-series victory.
The visitors chased down the total set by the hosts, reaching 131-5 after 21.2 overs to claim the win.
Lorcan Tucker led his side from the crease but could not prevent a collapse that saw them dismissed for 129 in 33.1 overs.
Jordan Neill contributed 33 runs off 25 balls, while Andrew Balbirnie added nine before falling to Jack Brassell's bowling.
Cade Carmichael started his innings brightly but was the first of three batsmen taken by Brassell throughout the match.
Harry Tector and Lorcan Tucker provided some resistance in the middle order, yet both were eventually removed.
JJ Smit took four wickets for just 20 runs, dismantling the Irish batting line-up with precision.
Louren Steenkamp reached 44 runs before being run out by Matthew Humphreys during the seventh over.
Michael van Lingen was dismissed for 15 by Jai Moondra early in the contest.
Matthew Humphreys claimed two further wickets, including that of Steenkamp, to reach his four-wicket figure.
The series outcome means Namibia have now won three out of five matches against Ireland in this competition.
This encounter served as preparation for next year's Cricket World Cup qualifier scheduled in the southern African nation in February.