diff --git a/.changesets/use-log_level-option-for-ruby-gem-logger.md b/.changesets/use-log_level-option-for-ruby-gem-logger.md
new file mode 100644
index 000000000..9b4ea47ff
--- /dev/null
+++ b/.changesets/use-log_level-option-for-ruby-gem-logger.md
@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "fix"
+---
+
+Use the `log_level` option for the Ruby gem logger. Previously it only configured the extension and agent loggers. Also fixes the `debug` and `transaction_debug_mode` option if no `log_level` is configured by the app.
diff --git a/lib/appsignal.rb b/lib/appsignal.rb
index 8e981ca67..c7ee74945 100644
--- a/lib/appsignal.rb
+++ b/lib/appsignal.rb
@@ -116,12 +116,7 @@ def start
       )
 
       if config.valid?
-        logger.level =
-          if config[:debug]
-            Logger::DEBUG
-          else
-            Logger::INFO
-          end
+        logger.level = config.log_level
         if config.active?
           logger.info "Starting AppSignal #{Appsignal::VERSION} "\
             "(#{$PROGRAM_NAME}, Ruby #{RUBY_VERSION}, #{RUBY_PLATFORM})"
@@ -230,12 +225,11 @@ def start_logger
       end
 
       logger.level =
-        if config && config[:debug]
-          Logger::DEBUG
+        if config
+          config.log_level
         else
-          Logger::INFO
+          Appsignal::Config::DEFAULT_LOG_LEVEL
         end
-
       logger << @in_memory_log.string if @in_memory_log
     end
 
diff --git a/lib/appsignal/config.rb b/lib/appsignal/config.rb
index 1ea1d437c..85574a29a 100644
--- a/lib/appsignal/config.rb
+++ b/lib/appsignal/config.rb
@@ -30,7 +30,6 @@ class Config
       :instrument_redis               => true,
       :instrument_sequel              => true,
       :log                            => "file",
-      :log_level                      => "info",
       :request_headers                => %w[
         HTTP_ACCEPT HTTP_ACCEPT_CHARSET HTTP_ACCEPT_ENCODING
         HTTP_ACCEPT_LANGUAGE HTTP_CACHE_CONTROL HTTP_CONNECTION
@@ -44,6 +43,20 @@ class Config
       :transaction_debug_mode         => false
     }.freeze
 
+    # @api private
+    DEFAULT_LOG_LEVEL = Logger::INFO
+    # Map from the `log_level` config option to Ruby's Logger level value.
+    #
+    # The trace level doesn't exist in the Ruby logger so it's mapped to debug.
+    # @api private
+    LOG_LEVEL_MAP = {
+      "error" => Logger::ERROR,
+      "warn" => Logger::WARN,
+      "info" => Logger::INFO,
+      "debug" => Logger::DEBUG,
+      "trace" => Logger::DEBUG
+    }.freeze
+
     ENV_TO_KEY_MAPPING = {
       "APPSIGNAL_ACTIVE"                         => :active,
       "APPSIGNAL_APP_NAME"                       => :name,
@@ -242,6 +255,18 @@ def []=(key, value)
       config_hash[key] = value
     end
 
+    def log_level
+      if config_hash[:debug] || config_hash[:transaction_debug_mode]
+        level = Logger::DEBUG
+      end
+      option = config_hash[:log_level]
+      if option
+        log_level_option = LOG_LEVEL_MAP[option]
+        level = log_level_option if log_level_option
+      end
+      level.nil? ? Appsignal::Config::DEFAULT_LOG_LEVEL : level
+    end
+
     def log_file_path
       path = config_hash[:log_path] || root_path && File.join(root_path, "log")
       if path && File.writable?(path)
diff --git a/spec/integration/diagnose b/spec/integration/diagnose
index a6f82cc61..2dbfbd962 160000
--- a/spec/integration/diagnose
+++ b/spec/integration/diagnose
@@ -1 +1 @@
-Subproject commit a6f82cc61025a53ccd2d00ca1ef2a1cf3478a00f
+Subproject commit 2dbfbd9621247c2dd1efb4f6932cf6960c67e203
diff --git a/spec/lib/appsignal/config_spec.rb b/spec/lib/appsignal/config_spec.rb
index 95dd607d7..dc51c7bad 100644
--- a/spec/lib/appsignal/config_spec.rb
+++ b/spec/lib/appsignal/config_spec.rb
@@ -171,7 +171,6 @@
         :instrument_redis               => true,
         :instrument_sequel              => true,
         :log                            => "file",
-        :log_level                      => "info",
         :name                           => "TestApp",
         :push_api_key                   => "abc",
         :request_headers                => [],
@@ -787,4 +786,83 @@
       end
     end
   end
+
+  describe "#log_level" do
+    let(:options) { {} }
+    let(:config) { described_class.new("", nil, options) }
+    subject { config.log_level }
+
+    context "without any config" do
+      it "returns info by default" do
+        is_expected.to eq(Logger::INFO)
+      end
+    end
+
+    context "with debug set to true" do
+      let(:options) { { :debug => true } }
+      it { is_expected.to eq(Logger::DEBUG) }
+    end
+
+    context "with transaction_debug_mode set to true" do
+      let(:options) { { :transaction_debug_mode => true } }
+      it { is_expected.to eq(Logger::DEBUG) }
+    end
+
+    context "with log_level set to error" do
+      let(:options) { { :log_level => "error" } }
+      it { is_expected.to eq(Logger::ERROR) }
+    end
+
+    context "with log_level set to warn" do
+      let(:options) { { :log_level => "warn" } }
+      it { is_expected.to eq(Logger::WARN) }
+    end
+
+    context "with log_level set to info" do
+      let(:options) { { :log_level => "info" } }
+      it { is_expected.to eq(Logger::INFO) }
+    end
+
+    context "with log_level set to debug" do
+      let(:options) { { :log_level => "debug" } }
+      it { is_expected.to eq(Logger::DEBUG) }
+    end
+
+    context "with log_level set to trace" do
+      let(:options) { { :log_level => "trace" } }
+      it { is_expected.to eq(Logger::DEBUG) }
+    end
+
+    context "with debug and log_level set" do
+      let(:options) { { :log_level => "error", :debug => true } }
+
+      it "the log_level option is leading" do
+        is_expected.to eq(Logger::ERROR)
+      end
+    end
+
+    context "with transaction_debug_mode and log_level set" do
+      let(:options) { { :log_level => "error", :transaction_debug_mode => true } }
+
+      it "the log_level option is leading" do
+        is_expected.to eq(Logger::ERROR)
+      end
+    end
+
+    context "with log level set to an unknown value" do
+      let(:options) { { :log_level => "fatal" } }
+
+      it "prints a warning and doesn't use the log_level" do
+        is_expected.to eql(Logger::INFO)
+      end
+
+      context "with debug option set to true" do
+        let(:options) { { :log_level => "fatal", :debug => true } }
+
+        it "prints a warning and sets it to debug" do
+          is_expected.to eql(Logger::DEBUG)
+        end
+      end
+    end
+  end
 end
diff --git a/spec/lib/appsignal_spec.rb b/spec/lib/appsignal_spec.rb
index a80853a17..c1a32b442 100644
--- a/spec/lib/appsignal_spec.rb
+++ b/spec/lib/appsignal_spec.rb
@@ -1236,7 +1236,7 @@ def initialize_config
           before do
             capture_stdout(out_stream) do
               initialize_config
-              Appsignal.config[:debug] = true
+              Appsignal.config[:log_level] = "debug"
               Appsignal.start_logger
             end
           end